Playwright E2E: stamp running test name into window title

[vdavid]

Adds beforeEach / afterEach hooks to apps/desktop/test/e2e-playwright/fixtures.ts that update the main Tauri window's OS title with the currently running test name, so you can see which spec is in flight (or stuck) by glancing at the dock / Cmd-Tab / Linux title bar — no log tailing needed.

• beforeEach: sets title to <base> (Running: Section › test name)
• afterEach: appends (FINISHED)
• The base title is captured once per worker on the first hook call, so suffixes don't accumulate across tests
• Test name is derived from testInfo.titlePath, joining describe block(s) + test title with ›
• Failures inside the hooks are swallowed — title decoration is for human eyeballs only and should never break a test
• Uses the standard plugin:window|set_title (and |title for the initial read), no new Rust command
• Permissions (core:window:allow-title, core:window:allow-set-title) are added to the auto-generated playwright.json capability that build.rs only emits when the playwright-e2e Cargo feature is on, so release builds are unaffected
• Each parallel shard owns its own Tauri instance + worker process, so the per-worker title state stays clean across shards
• apps/desktop/test/e2e-playwright/CLAUDE.md documents the new behavior

Test plan

• cargo check --features playwright-e2e clean; verified the regenerated playwright.json includes the two new permissions
• tsc --project test/e2e-playwright/tsconfig.json clean
• eslint test/e2e-playwright/fixtures.ts clean
• Manual verification of the title change will happen on the next local ./scripts/check.sh --check desktop-e2e-playwright run; if the set_title invoke ever rejects (e.g., permissions slip out of sync) the hooks swallow the error so tests still pass — failure mode is just "title doesn't update," not a flaky test