chore: Implement Watchdog process for reliable telemetry

[ergunsh]

This PR implements the watchdog process architecture for the telemetry system. It moves the ClearcutSender execution to a dedicated child process, ensuring that events—especially shutdown events—are reliably transmitted even if the main server process terminates abruptly.

Added an e2e test that runs the server, checks the log file and confirms the telemetry logs exist and that the watchdog process is correctly killed after sending the shutdown event once the main process is killed.

Implementation Roadmap:
This is the fourth in a series of PRs designed to implement the telemetry system:

1. CLI & Opt-out Mechanism (Merged):
   • Added --usage-statistics flag and transparency logging.
2. Logger Scaffolding & Integration (Merged):
   • ClearcutLogger: Implemented the main logging entry point.
   • One-way Data Flow: Integrated logToolInvocation and logServerStart hooks into main.ts to capture events.
   • ClearcutSender: Introduced a transport abstraction.
   • Type Definitions: Added TypeScript definitions for the telemetry Protocol Buffer messages.
3. Persistence Layer (Merged):
   • FilePersistence: Implemented a local file-based state manager to persist the lastActive timestamp.
   • Daily Active Logic: Integrated persistence into ClearcutLogger to automatically detect and log daily_active events (with days_since_last_active calculation) via logDailyActiveIfNeeded.
4. Watchdog Process Architecture (This PR):
   • WatchdogClient: Added a client-side wrapper to spawn and communicate with the watchdog process via stdin.
   • watchdog/main.ts: Created the entry point for the watchdog process. It listens for IPC messages and uses ClearcutSender to transmit events.
   • Reliable Shutdown: The watchdog monitors the parent process and guarantees a shutdown event is sent when the parent exits or crashes (detecting stdin closure).
   • Refactoring: Moved ClearcutSender to the watchdog directory and updated ClearcutLogger to delegate event sending to the WatchdogClient.
5. Transport, Batching & Retries (Next):
   • Finalize ClearcutSender with actual HTTP transport logic, including event batching and exponential backoff retries.