feat: add heartbeat_tick tool for automated task pickup (#13) (#14)

Adds heartbeat_tick tool that automates task pickup across all projects:

- Runs session health checks (zombie cleanup) before pickups
- Loops over all registered projects
- Picks up tasks by priority (To Improve > To Test > To Do)
- Supports two work modes:
  - parallel: each project can have DEV+QA running independently
  - sequential: only 1 DEV + 1 QA globally (can be different projects)
- Respects per-project maxDevWorkers/maxQaWorkers settings
- Supports dryRun mode and maxPickups limit
- Context guard: only works from DM/cron, blocks project groups

Also adds:
- workMode config option (parallel | sequential)
- maxDevWorkers/maxQaWorkers fields to Project type

lib/projects.ts

@@ -23,6 +23,8 @@ export type Project = {
   baseBranch: string;
   deployBranch: string;
   autoChain: boolean;
+  maxDevWorkers?: number;
+  maxQaWorkers?: number;
   dev: WorkerState;
   qa: WorkerState;
 };