feat(meet-kevin): pipeline orchestrator + service main loop
Implements Task 8 of the Meet Kevin revival plan.
- pipeline.py: PipelineDeps dataclass (frozen, DI-friendly), process_one_video
state machine (discovered→captioned→analyzed with retry/cost-cap logic),
and daily_cost_used() SQL helper.
- main.py: async run() entry point with RSS poll loop, per-video pipeline
processing, OTEL counters, SIGTERM/SIGINT shutdown, httpx client lifecycle,
and clean Anthropic/DB teardown.
- tests: 5 pipeline unit tests (happy path, no captions, cost cap, retry
increment, failed-after-3-retries) all passing; full watcher suite 56/56.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>