perf(electron): optionally unload renderer on close (4/8)

[backryun]

Summary

• add a persisted tray policy for keeping the dashboard loaded or unloading its renderer on close
• keep the embedded/remote proxy server, tray, and main-process update flow alive in unload mode
• recreate the renderer from tray open, tray double-click, a second app launch, or macOS activation
• restore only same-origin dashboard URLs and rely on Electron's persistent default session for auth state
• keep keep-loaded as the default, preserving the existing fast-reopen behavior

Closes the Stage 4 implementation slice tracked by #10321.

Measured behavior

Measured on macOS arm64 with an isolated Electron profile and a lightweight remote dashboard fixture:

State	Electron processes	RSS
Renderer loaded	5	531.4 MiB
Renderer unloaded	4	436.5 MiB

• observed reduction while closed: 94.9 MiB and one renderer process
• renderer recreation: 74 ms in the persisted-policy validation run
• restored URL: /dashboard/settings?stage4=1
• restored session: the second request retained stage4_session=preserved

These numbers isolate shell/renderer overhead with a lightweight page; production dashboard totals will vary. The active app has no custom deep-link protocol (omniroute:// was previously removed because no handler existed), so there is no deep-link state to restore. External-link handling is unchanged. Auto-update listeners remain in the main process and renderer notifications safely no-op while the window is absent.

Validation

• node --import tsx/esm --test tests/unit/electron*.test.ts tests/unit/build/electron-release-latest-yml.repro.test.ts — 134 passed
• npm run test:vitest — 357 passed
• npm run check:file-size — passed
• node --check electron/main.js electron/lib/remoteServerPreferences.js electron/lib/windowClosePolicy.js — passed
• pre-commit formatting, ESLint, docs sync, artifact, and type-budget gates — passed

Full-repository npm run lint remains blocked by pre-existing errors in @omniroute/opencode-plugin/src/index.ts and tests/unit/cli-env-inline-comment-10100.test.ts; neither file is changed here.

[mergify]

⚠️ The sha of the head commit of this PR conflicts with #10327. Mergify cannot evaluate rules on this PR. Once #10327 is merged or closed, Mergify will resume processing this PR. ⚠️

[diegosouzapw]

IN-FLIGHT — deferido. O head desta PR está no checkout principal concorrente (perf/electron-unload-on-close). Não faço merge, rebase, push nem alteração nesse checkout.