PDF upload, gallery → assets with type tabs, orphan detection fix

PDF upload support:
* index.php: application/pdf added to $mimeMap + $extMap in the
  /api/upload handler. PDFs are stored in uploads/ like images/audio.
* editor.js uploadFile(): detects PDF via MIME or .pdf extension.
  Inserts a markdown link [📄 filename](uploads/...) instead of an
  image embed. Paste + drop handlers updated to accept PDFs.
* index.php: new toolbar button #md-upload-pdf with ph-file-pdf icon
  next to the extract button. Triggers a hidden file input
  (accept=".pdf"). Wired in editor.js.

Gallery → Assets rename:
* index.php footer button: "Images" → "Assets", icon ph-folder-open.
* index.php gallery overlay header: "images" → "assets", icon
  ph-folder-open, upload input accept extended to include .pdf.
* Empty state text: "no images" → "no assets".

File-type tabs in the assets overlay:
* index.php: new #gallery-tabs div with 4 buttons (All / Images /
  Audio / PDF), each with data-filter attribute.
* gallery.js: fileType(url) helper returns 'image'|'audio'|'pdf'|
  'other'. Tab clicks toggle .active class and filter gallery-items
  by data-url + fileType. activeFilter persists across re-opens.
* CSS: .gallery-tab styling with hover + .active accent fill.

PDF rendering in the assets grid:
* gallery.js mediaTile(): PDFs render as ph-file-pdf icon + filename
  instead of a thumbnail. Orphaned PDFs show the same icon tile.
* Click on an orphaned PDF opens it in a new tab (window.open).
* "New card" from an orphaned PDF inserts a markdown link (not
  image embed).

Orphan detection fix (gallery.js):
* Root cause: loadCards() in app.js uses two-phase lazy loading —
  first /api/cards/meta (body=null on all cards), then batches of 25
  with full bodies. Opening the gallery before the last batch
  completes meant most cards had body=null, getReferencedUrls()
  found no URLs, and every file appeared orphaned.
* Fix: openGallery() now fetches its own card list with full bodies
  via api('api/cards') in parallel with api('api/uploads'), stored in
  a module-local galleryCards array. Both getReferencedUrls() and
  findCardForUrl() read from galleryCards instead of state.cards.
* Bonus: added a fallback regex uploads/[hex]{32}.[ext] that catches
  references in any format the specific patterns might miss (HTML
  attributes, custom blocks, inline text).

chore: bump version to 0.9.18

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

public/index.php

@@ -454,8 +454,8 @@ if (str_starts_with($route, '/api/')) {
         }
 
         // Check MIME — finfo first, fallback to extension for audio
-        $mimeMap = ['image/png' => 'png', 'image/jpeg' => 'jpg', 'image/gif' => 'gif', 'image/webp' => 'webp', 'audio/mpeg' => 'mp3', 'audio/ogg' => 'ogg', 'audio/wav' => 'wav', 'audio/x-wav' => 'wav', 'audio/mp4' => 'm4a', 'application/ogg' => 'ogg'];
-        $extMap = ['mp3' => 'mp3', 'ogg' => 'ogg', 'wav' => 'wav', 'm4a' => 'm4a'];
+        $mimeMap = ['image/png' => 'png', 'image/jpeg' => 'jpg', 'image/gif' => 'gif', 'image/webp' => 'webp', 'audio/mpeg' => 'mp3', 'audio/ogg' => 'ogg', 'audio/wav' => 'wav', 'audio/x-wav' => 'wav', 'audio/mp4' => 'm4a', 'application/ogg' => 'ogg', 'application/pdf' => 'pdf'];
+        $extMap = ['mp3' => 'mp3', 'ogg' => 'ogg', 'wav' => 'wav', 'm4a' => 'm4a', 'pdf' => 'pdf'];
         $finfo = new finfo(FILEINFO_MIME_TYPE);
         $realMime = $finfo->file($file['tmp_name']);
         $ext = $mimeMap[$realMime] ?? null;
@@ -1236,7 +1236,7 @@ if (str_starts_with($route, '/api/')) {
                     <i class="ph ph-calendar-dots text-sm"></i><span class="font-pixel text-[10px]">Calendar</span>
                 </button>
                 <button id="gallery-btn" class="flex items-center gap-2 px-2.5 py-1.5 text-xs border border-t-border text-t-muted hover:border-t-accent hover:text-t-accent transition-colors">
-                    <i class="ph ph-image-square text-sm"></i><span class="font-pixel text-[10px]">Images</span>
+                    <i class="ph ph-folder-open text-sm"></i><span class="font-pixel text-[10px]">Assets</span>
                 </button>
                 <button id="tasks-btn" class="flex items-center gap-2 px-2.5 py-1.5 text-xs border border-t-border text-t-muted hover:border-t-accent2 hover:text-t-accent2 transition-colors">
                     <i class="ph ph-check-square-offset text-sm"></i><span class="font-pixel text-[10px]">Tasks</span>
@@ -2027,18 +2027,24 @@ if (str_starts_with($route, '/api/')) {
     </div>
 
 
-    <!-- Gallery -->
+    <!-- Assets (was Gallery) -->
     <div class="overlay fixed inset-0 z-[72]" style="background:var(--t-overlay)" id="gallery">
         <div class="bg-t-surface border border-t-border rounded-sm shadow-2xl flex flex-col absolute" style="inset:40px;">
             <div class="flex items-center gap-3 px-4 py-3 border-b border-t-border shrink-0">
-                <i class="ph ph-images text-t-accent text-base"></i>
-                <h2 class="font-pixel text-xs text-t-accent">images</h2>
+                <i class="ph ph-folder-open text-t-accent text-base"></i>
+                <h2 class="font-pixel text-xs text-t-accent">assets</h2>
                 <span id="gallery-count" class="font-pixel text-[9px] text-t-dim"></span>
+                <div id="gallery-tabs" class="flex items-center gap-1 ml-3">
+                    <button class="gallery-tab active font-pixel text-[9px] px-2 py-0.5 border border-t-border text-t-muted transition-colors" data-filter="all">All</button>
+                    <button class="gallery-tab font-pixel text-[9px] px-2 py-0.5 border border-t-border text-t-muted transition-colors" data-filter="image">Images</button>
+                    <button class="gallery-tab font-pixel text-[9px] px-2 py-0.5 border border-t-border text-t-muted transition-colors" data-filter="audio">Audio</button>
+                    <button class="gallery-tab font-pixel text-[9px] px-2 py-0.5 border border-t-border text-t-muted transition-colors" data-filter="pdf">PDF</button>
+                </div>
                 <div class="flex-1"></div>
                 <button id="gallery-upload" class="flex items-center gap-1.5 px-2.5 py-1 text-xs border border-t-border text-t-muted hover:border-t-accent hover:text-t-accent transition-colors">
                     <i class="ph ph-upload-simple text-sm"></i><span class="font-pixel text-[10px]">Upload</span>
                 </button>
-                <input type="file" id="gallery-upload-file" accept="image/*,audio/*" multiple class="hidden">
+                <input type="file" id="gallery-upload-file" accept="image/*,audio/*,.pdf,application/pdf" multiple class="hidden">
                 <button id="gallery-close" class="flex items-center gap-1.5 px-2.5 py-1 text-xs border border-t-border text-t-muted hover:border-t-danger hover:text-t-danger transition-colors">
                     <i class="ph ph-x text-sm"></i><span class="font-pixel text-[10px]">Close</span>
                 </button>
@@ -2140,6 +2146,8 @@ if (str_starts_with($route, '/api/')) {
                 <button data-md="hr" title="Divider" class="toolbar-btn"><i class="ph ph-minus text-sm"></i></button>
                 <div class="w-px h-4 bg-t-border mx-1"></div>
                 <button data-md="extract" title="Extract selection to new card" class="toolbar-btn"><i class="ph ph-scissors text-sm"></i></button>
+                <button id="md-upload-pdf" title="Upload & link PDF" class="toolbar-btn"><i class="ph ph-file-pdf text-sm"></i></button>
+                <input type="file" id="md-upload-pdf-file" accept=".pdf,application/pdf" class="hidden">
                 <?= PluginManager::instance()->slot('md-toolbar') ?>
                 <div class="flex-1"></div>
                 <button id="toggle-lines" class="toolbar-btn flex items-center gap-1.5 px-2" title="line numbers"><i class="ph ph-hash text-sm"></i></button>