test(runtime): cover command and capture boundaries

[yashranaway]

Progresses #36

Summary

• cover click, fill, press, scroll, state, and both tour paths against semantic controls
• verify fill results never echo values and unsafe links remain blocked
• lock viewport and section screenshot plans to their 80-point cap, bottom anchor, and 96 px deduplication
• cover budget pruning's text-chop fallback and retain stale-reference assertions

Verification

• npx --yes pnpm@9.15.0 test:runtime
• CI-equivalent Swift 6.1 container: 36/36 protocol tests plus MCP integration passed
• git diff --check