feat: channel permissions UI, DM Sans font, private channel filtering, migration fix

- Rewrite ChannelSettingsModal with full tri-state permission override UI
  for roles and members (allow/neutral/deny per permission bit)
- Switch font from Inter to self-hosted DM Sans (woff2 variable fonts)
- Add client-side VIEW_CHANNEL filtering in ChannelSidebar for private channels
- Broadcast isPrivate flag on channel override changes
- Fix voice permission bit migration: gate behind persistent flag to prevent
  repeated re-runs that stripped STREAM from @everyone roles
- Add speakingUserIds set to voice store for efficient user-level lookups
- Clear current channel view when a channel is deleted
- Move .glass-strip to @layer utilities for proper CSS specificity
- Simplify avatar initials font size to proportional formula

packages/web/src/styles/globals.css

@@ -138,7 +138,7 @@
   /* ── Glass Material Tiers ──
    * .glass        — Popovers, context menus, autocomplete (small, no backdrop)
    * .glass-modal  — Center-screen dialogs (large, with backdrop, higher opacity for legibility)
-   * .glass-strip  — Space sidebar edge (no border-radius, directional shadow)
+   * .glass-strip  — Space sidebar edge (moved to @layer utilities to win over bg-surface-* utilities)
    * .glass-bubble — Persistent floating controls (voice bar, input pill)
    * .glass-pill   — Inline decorations (reactions, tags, lighter blur)
    *
@@ -159,17 +159,6 @@
     transition: border-color 0.2s ease, box-shadow 0.2s ease;
   }
 
-  /* Space strip glass — no border-radius, rightward shadow */
-  .glass-strip {
-    backdrop-filter: blur(20px) saturate(120%);
-    -webkit-backdrop-filter: blur(20px) saturate(120%);
-    background: var(--glass-bg);
-    border-right: 1px solid rgba(255, 255, 255, 0.05);
-    box-shadow:
-      inset 0 1px 0 rgba(255, 255, 255, 0.03),
-      2px 0 12px rgba(0, 0, 0, 0.20);
-  }
-
   /* Floating bubble glass — bottom bar, input pill */
   .glass-bubble {
     backdrop-filter: blur(20px) saturate(120%);
@@ -247,6 +236,17 @@
 }
 
 @layer utilities {
+  /* Space strip glass — in utilities layer so md:glass-strip wins over bg-surface-* */
+  .glass-strip {
+    backdrop-filter: blur(20px) saturate(120%);
+    -webkit-backdrop-filter: blur(20px) saturate(120%);
+    background: var(--glass-bg);
+    border-right: 1px solid rgba(255, 255, 255, 0.05);
+    box-shadow:
+      inset 0 1px 0 rgba(255, 255, 255, 0.03),
+      2px 0 12px rgba(0, 0, 0, 0.20);
+  }
+
   .rounded-inherit {
     border-radius: inherit;
   }