feat(tasks): wire the task tools into role_pipeline

Tool availability is a strict per-stage allowlist, so the task doctrine was
inert in role_pipeline — no stage granted the tools. Add them where they fit
each stage's tier and role, and point the stage prompts at the lifecycle:

- analyst (read-only): task_search/task_context to find related or duplicate
  work and ground the analysis.
- implementer: full set — claim before working, submit_for_review once
  verification passes, create one if the work warrants tracking.
- reviewer: task_context to judge against the task's own criteria, task_update
  to complete it on an approved verdict.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/workflows/prompts/analyst.md

@@ -8,7 +8,10 @@ Steps:
 1. Read the user's request carefully. Restate what is actually being asked.
 2. Use `file_read` and shell (read-only: `ls`, `grep`, `cat`, `find`) to locate the relevant
    code. Identify the files, modules, and subsystems involved. Do not modify anything.
-3. Derive concrete, checkable requirements and acceptance criteria.
+3. Check for existing work: `task_search` for related, duplicate, or blocking tasks, and
+   `task_context` to load any the request names. Fold what you find into the analysis rather
+   than re-deriving it; flag a duplicate instead of restating it.
+4. Derive concrete, checkable requirements and acceptance criteria.
 
 The decision history above (steering, approvals, prior verdicts) is ground truth — honour it.