Prevent duplicate session browser controllers

[Pimpmuckl]

Summary

• acquire one PID-backed controller lease per ask-pro session directory
• recover dead owners with atomic lease-directory takeover and retire leases atomically on release
• keep recursive fresh/resume transitions inside the outer lease while preserving cross-session concurrency

Validation

• plugin validator
• pnpm run build
• pnpm run lint
• pnpm test (17 files, 281 tests)
• pnpm run format:check
• pnpm pack --dry-run
• Review Suite fast: rvw_f7ee59d9, clean and closure-conformant