Browser-mode test parity for Tauri & Dioxus

[goosewobbler]

Summary

Browser mode (#260) shipped for Tauri, Electron, and Dioxus, but test coverage is asymmetric. Electron has the full pyramid (unit → integration → E2E → package); Tauri and Dioxus only have unit tests + package fixtures. This issue brings Tauri and Dioxus up to the Electron template so all three are gated equally.

Current state

Tier	Electron	Tauri	Dioxus
Unit	✅	✅	✅
Integration	✅ test/integration/browser-mode.integration.spec.ts, launcher.browser.integration.spec.ts	❌ none	❌ none
E2E	✅ e2e/wdio.electron-browser.conf.ts + e2e/test/electron-browser/mock.spec.ts	❌ no config	❌ no config
Package	✅ (CJS+ESM, mocking exercised)	✅ but mocking only	⚠️ fixtures/package-tests/dioxus-app/test-browser/browser.spec.ts only checks page load + service presence — no mocking

Tasks

• Tauri integration tests — mirror Electron's browser-mode.integration.spec.ts / launcher.browser.integration.spec.ts: launcher→worker handshake, capability transformation, no-driver assertion, navigation re-injection, mock lifecycle across navigation.
• Dioxus integration tests — same template.
• Tauri E2E — add e2e/wdio.tauri-browser.conf.ts + a browser-mode spec (real Chrome, IPC mock, ps-based process-absence check that no tauri-driver/msedgedriver started).
• Dioxus E2E — add an equivalent browser-mode E2E config + spec.
• Dioxus package fixture — extend fixtures/package-tests/dioxus-app/test-browser/browser.spec.ts to actually exercise browser.dioxus.mock() + mock.update(), matching the Tauri/Electron fixtures.
• Dioxus docs — add a one-line note to packages/dioxus-service/docs/browser-mode.md that events are unsupported (no native event bus; see native-types/src/dioxus.ts), so the docs match Tauri/Electron's events sections by explicit omission.
• Wire the new Tauri/Dioxus browser-mode E2E configs into CI (the existing electron-browser E2E + the three :browser package tests are wired separately as part of closing Browser-only test mode for Tauri and Electron services #260).

Notes

• Reuse the Electron integration/E2E specs as the canonical template — the worker flow (navigate → inject → patch url() → single-context mock) is identical across frameworks.
• Dioxus has no event bus, so there's intentionally no events tier to test (unlike Tauri/Electron).

Follow-up to #260.