feat(chromium): dispatch trusted CDP input

[yashranaway]

Closes #34

Summary

• keep semantic target resolution and unsafe-link enforcement in the isolated agent world, then dispatch Chromium mouse/key/text actions through CDP
• support common navigation/editing keys plus validated character input without changing the portable click / fill / press verbs
• declare trusted-cdp versus WebKit synthetic-dom in machine-readable capabilities
• add a real Chromium fixture proving click, input, and key handlers receive isTrusted: true
• document the implemented Phase 4 fidelity boundary and preserve the rule that fill values are never echoed or recorded

Validation

• pnpm test:runtime
• pnpm test:e2e:linux (44/44 protocol tests, cross-engine conformance, trusted-input fixture, full Linux P2 flow)
• git diff --check