fix(security+audit): strip latent RCE grants, opener allowlist, GDI leaks, CI hardening

From the deep-audit wave (reviewer-verified: capability identifiers valid, no
removed-crate references, GDI free ordering correct):

- Removed 8 never-registered plugins (clipboard-manager, fs, shell, http,
  process, os, dialog, global-shortcut) from Cargo.toml AND their capability
  grants (shell:allow-execute, unscoped fs writes, http:default, …) — verified
  the web never invokes any of them. A latent RCE-class surface is gone.
- on_new_window: only http/https/mailto reach the OS opener (file:///custom
  schemes previously bypassed the opener capability scope entirely).
- set_badge_count: freed hdc + hdc_screen on all three GDI error paths
  (leaked per badge update in a long-running tray app).
- 8s reveal failsafe gated by an AtomicBool: no longer re-shows a window the
  user closed to tray; page-load reveal now fires once only (logout reloads
  don't re-surface a tray-hidden window); recovery for a missed page-load
  event preserved.
- toast.rs: store pruned on Activated too + capped at 20 (was unbounded).
- Startup no longer panics when the bundled icon is missing (tray skipped
  gracefully); msSmartScreenProtection no longer disabled (throttling
  disables kept); rust-version corrected to 1.77.2.
- release.yml update-manifest: fails on empty signatures (was: could publish
  a manifest that traps Windows users in a failed-update loop); partial-
  failure window documented. Deleted the stale upstream tauri.yml workflow.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src-tauri/capabilities/desktop.json

@@ -10,7 +10,6 @@
   ],
   "permissions": [
     "updater:default",
-    "global-shortcut:default",
     "deep-link:default"
   ]
 }