feat(cua-driver): centralize protected resource grants per runtime

[f-trycua]

Summary

Hoists protected-consent ownership to the canonical runtime registry and adds the generic resource-grant coordinator required by #2385. Browser and future desktop/file adapters share one runtime-owned broker, exact canonical resource digests, per-runtime/session/mode/policy binding, TTLs, indicator liveness, and teardown revocation.

Security contract

• Provider identity is runtime-owned, never process-global first-writer state.
• Raw paths, typed text, page content, selectors, and screenshot data are never retained as grant keys.
• Standard uses protected consent; bounded activates an indicator only after its immutable manifest admitted the call; unrestricted skips Cua prompts without widening policy.
• Session teardown and runtime drop revoke covered grants.
• This slice does not activate new capability groups.

Verification

• Focused broker, digest, reuse, expiry, revocation, provider-failure, and cross-runtime tests pass locally.
• Cross-platform Rust compilation passes.
• Full CI and stacked exact-SHA evidence will be completed before this PR is marked ready.

Stacked on #2576 and #2575. Progresses #2385.