fix(supervise): preflight bridge roots before dispatch

[drewstone]

Summary

• Refuse unroutable and full bridge work before remote run allocation.
• Record pre-dispatch attempts as known zero spend and keep cancellation abort-aware.
• Remove the implicit supervisor lifecycle deadline; callers opt in with timeoutMs.

Verification

• pnpm exec vitest run src/runtime/supervise/bridge-executor.test.ts tests/kernel/supervise-full-profile-bridge.test.ts src/runtime/supervise/interactive-worker.test.ts --maxWorkers=3 --fileParallelism=true — 96 passed
• pnpm run api:surface
• pnpm run docs:freshness
• pnpm run check:version-bump
• git diff --check