Isolate browser bridge cleanup

[nicodes]

Production diagnostics policy and browser-verification layer for https://github.com/aviorstudio/fieldsofrevik/issues/148. Native stack #17; depends on #15.

Acceptance evidence

Source head after the native-stack replay onto merged #15: a8b89a1f705ccca82cea27087600ad5b82ad49ba (tree-identical to pre-replay 8582a7898676f88eff7bf4e9d683344de30e3e67).

Criterion	Evidence
Preserve debug consumers while ordinary production exports expose no bridge	Godot policy tests pass. The exact packaged ZIP was installed into a clean fixture and exported with Godot 4.7.2; playwright-cli observed no godotElements, godotEvents, godotTestState, or owner global despite enabled/test-mode settings.
Explicit production diagnostics feature and distinct artifact identities	Diagnostic export uses custom feature gd_playwright_diagnostics. Exact-head CI release-export identities were distinct: ordinary 62aa0cf7037d062be4d53058f0c00146a1c25807dab0ea84e7379013d62cbcfb; diagnostic 4ef999af717bb25da97c867833baa25a6754ec80ee89a00b38409da9097bc757.
Safe read-only data contract	Exact/prefix element rules and event/state field rules default deny in diagnostic releases. Browser assertions accepted start_button/route, rejected undeclared entries and nested token, and rejected non-JSON values in focused Godot tests. This is bounded validation, not a confidentiality guarantee.
Bridge cleanup/isolation and ordinary Playwright input	Browser assertions proved stale/disposable owners cannot clear a newer owner, owner cleanup removed globals, and a normal canvas click changed the allowlisted observed state without adding gameplay setters.
CI/release gate	Common CI and both release targets now install SHA-512-verified Godot 4.7.2 export templates, pinned playwright-cli 0.1.18/Playwright Chromium, export both release artifacts from the exact ZIP, run browser assertions, and upload screenshots/identities. Replayed exact-head CI: PASS — https://github.com/aviorstudio/gd-playwright/actions/runs/34732370313; downloaded CI screenshots and identities were personally inspected.

Ordinary release artifact

Diagnostic release artifact

Local verification

• Go 1.24.13: go test ./... — PASS.
• Bun 1.2.23: bun test — 5 tests, 14 assertions, PASS.
• Godot 4.7.2: four addon scripts, payload policy tests, and 8 runner controls — PASS.
• Exact ZIP lifecycle: enable/restart/disable/restart and consumer-owned settings/autoload preservation — PASS.
• Exact ZIP SHA-256: 43b086fe617324dae171336b13a552affa496aa5a8ea1016ba0d22e3f44a8969.
• Installed-tree SHA-256: 2b665e540e9f5069088e0c15ca637921e8c3ded30c8b0cd0e1611c9adda58ba3.
• Browser: playwright-cli 0.1.18, ordinary and diagnostic Godot 4.7.2 release exports — PASS; named session closed.
• actionlint 1.7.7, ShellCheck 0.11.0, and git diff --check — PASS.

No reviewer is requested under Team No Review.