fix(mcp): share CLI timeout derivation

[yashranaway]

Closes #29.

What changed

• Move command timeout derivation into shared HeadlessProtocol code.
• Make both the CLI and stdio MCP adapter call that one helper.
• Preserve the existing CLI bounds for normal commands, waits, tours, screenshots, screenshot series, and recording stop.
• Mark backlog C1 complete.

This fixes MCP calls such as wait --timeout 90000, which previously inherited a flat 30-second socket timeout despite requesting a valid 90-second wait.

Verification

• pnpm test:runtime: passed.
• Swift 6.1 protocol/security suite in Docker: 31/31 passed.
• Explicit Linux build of the headless product: passed.
• Explicit Linux build of the headless-mcp product: passed.
• git diff --check: passed.