[loop cycle 2] fix(notifications): forward service-worker showNotification to native toast

[karem505]

What

Fixes a class of missing notifications. WhatsApp Web raises some notifications through the service worker via ServiceWorkerRegistration.showNotification(...) (used when it treats the tab as backgrounded). The existing window.Notification shim only intercepts the page-side new Notification(...) constructor — so the service-worker path slipped past it and those notifications never reached the OS notification center.

How

In bridge.js (section 2b, right after the existing Notification shim), override the page-side ServiceWorkerRegistration.prototype.showNotification to forward through the same native notify command the constructor shim already uses, and stub getNotifications() to resolve to [] (we render native toasts, so there's no in-page Notification object to return).

• Installed as a Tauri initialization_script, so it runs before any page JS → WhatsApp can't capture a pre-patch reference; prototype lookup at call time means instances created later are covered.
• Origin-guarded (whole file is gated to https://web.whatsapp.com) and wrapped in its own try/catch, so it can never abort the rest of bridge.js.
• Routes through commands::notify, inheriting its lock-screen and settings suppression unchanged.
• Scope is honest: notifications fired from inside the service worker's own realm can't be reached by a page-injected script (documented in the comment).

Verification

Gate 1 — deterministic (cargo build --locked + cargo test): PASS (51 tests; bridge.js is embedded via include_str!).

Gate 2 — real-engine behavioral (PyGObject WebKitGTK 2.x harness, origin spoofed to web.whatsapp.com): PASS. With a __TAURI__.invoke recorder installed:

• new Notification("DM from Sara",{body:"hey there"}) → 1 notify invoke ✅
• reg.showNotification("Group: Family",{body:"3 new messages"}) → 1 notify invoke ✅
• showNotification returns a Promise ✅ · getNotifications() → [] ✅ · Notification.permission === "granted" ✅ (no regression to the existing path)

Gate 3 — generation-blind code review (separate feature-dev:code-reviewer): APPROVE, severity none, no must-fix. Confirmed: override timing prevents a pre-patch reference; both paths inherit identical Rust-side suppression; try/catch isolated; getNotifications stub redundant-but-harmless; tag-dedup absence is pre-existing (matches the window.Notification shim), not a regression.

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🤖 PR-ONLY — do not auto-merge. Releasing whatRust is manual via a v* tag; this loop never merges, bumps the version, or tags a release. Opened by the whatrust-fix-loop (cycle 2/6).