relay: burger menu for mobile, admin reachable, badge matches header buttons

The relay's nav row used to flatten on mobile by hiding admin / user
identity / compose buttons outright, leaving only "account" + "logout".
Admin was completely unreachable from a phone. Replaces that with a
proper burger menu and exposes every nav target.

* layout.php: new <button id="nav-burger"> with a ph-list icon between
  the spacer and #nav-buttons. Inline `style="display:flex"` removed
  from #nav-buttons — display is now CSS-driven, so the burger
  popover and the desktop row don't fight each other.
* app.js showView(): the mobile-block on `name === 'admin'` is gone.
  Burger button visibility is now mirrored against the same
  setup/login/change-password gating that hides #nav-buttons. Picking
  any view also clears `.menu-open` so the popover collapses behind
  the freshly-shown view.
* app.js toggleNavMenu(): exposed on window for the inline onclick.
  Document-level click outside closes the menu.
* style.css: default `#nav-buttons:not(.hidden)` becomes flex (same
  semantics as the old inline). #nav-burger is `display:none` on
  desktop, `inline-flex` on mobile. Mobile media query drops the old
  display:none rules for #nav-admin / #view-admin / #nav-compose,
  keeps #nav-user hidden (redundant with the menu), and adds a
  `.menu-open` rule that turns #nav-buttons into a popover anchored
  to the header (position:absolute, right:12px, surface bg, border,
  shadow, z-index 50). Buttons inside the popover go full-width
  left-aligned. header { position:relative } so the absolute
  positioning has an anchor.
* style.css: also #view-admin .section gets a simple display:block
  override on mobile so the desktop grid-area layout doesn't break
  the page when admin is opened from a phone.

header .user .badge sizing (carried over from the previous turn): the
admin badge in the relay header now matches the .nav-btn box-model
exactly (5px 10px padding, 9px font, 1px border, 3px radius, line-
height:1, pixel font), so it sits flush with the nav buttons instead
of being a tiny pill in the middle of the row.

chore: bump version to 0.9.8

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

config.php

@@ -1,7 +1,7 @@
 <?php
 
 define('APP_NAME', 'hyprcrd');
-define('APP_VERSION', '0.9.7');
+define('APP_VERSION', '0.9.8');
 
 // Database path — writable directory, outside webroot
 define('DB_PATH', __DIR__ . '/data/hyprcrd.db');