Support ~/work as a second Pipeline domain

Add multi-domain support to Pipeline so it can run against ~/work independently from the omnirepo.

Changes needed

1. TASK_DB_PATH support in Pipeline — Pipeline should accept a --task-db flag (or config field) that sets TASK_DB_PATH when spawning agents. The task CLI already supports TASK_DB_PATH env var, so this is just plumbing it through. Initialize a new DB at ~/work/tasks.db with: TASK_DB_PATH=~/work/tasks.db task init

2. Auto-discover AGENTS.md from pcRepoRoot — The dev prompt builder (Dev.buildDevPrompt) currently injects omni-specific context. It should auto-discover <pcRepoRoot>/AGENTS.md instead of hardcoding omni's path. Optionally expose a --agents-md flag for explicit override.

3. CODEROOT / pcRepoRoot — Already configurable. Just needs to be set to ~/work when running for that domain. No code changes required, just config/docs.

4. Run config for ~/work domain — Document or create a config entry (e.g. in fund domain registry or a shell alias) so the user can launch a Pipeline instance pointed at ~/work with the correct CODEROOT, TASK_DB_PATH, and AGENTS.md.

Out of scope

• Full domain registry / fund integration (that comes later)
• Any scheduler changes
• Isolation guarantees between domains (informal phase)

Goal

After this task, the user should be able to run two Pipeline instances: one for omnirepo and one for ~/work, each with their own task DB and AGENTS.md context.