feat(TASK-005): wire project state and agent handoff into start/complete commands

- Add update_project_state() helper: updates Current Task + Last Updated
  in PROJECT_STATE.md via regex sub, preserving all surrounding formatting.
- Add update_agent_handoff() helper: updates Current Stage + Current Task
  sections in AGENT_HANDOFF.md, auto-detected from project_stage().
- Wire both helpers into rdb start TASK-ID and rdb complete TASK-ID CLI
  commands so task lifecycle transitions propagate to all control files.
- ADDING test_status.py with 5 tests: update_project_state task/timestamp
  updates, missing-file false return, agent handoff update and miss.

Acceptance criteria met:
- rdb start/complete now update PROJECT_STATE.md
- rdb start/complete now update AGENT_HANDOFF.md
- RUN_LOG.md already updated (pre-existing)
- Task formatting preserved (regex sub targets single line only)

TASKS.md

@@ -75,7 +75,7 @@ Acceptance Criteria:
 
 ## TASK-005 — Task lifecycle commands
 
-Status: Todo
+Status: Done
 
 Goal:
 Allow tasks to be managed from the CLI rather than manually editing TASKS.md.
@@ -94,3 +94,19 @@ Acceptance Criteria:
 - Preserves task formatting
 - Add/update tests
 - Run python -m pytest
+
+## TASK-007 — Improve generated agent prompts
+
+Status: Todo
+
+Goal:
+Make `rdb prompt` produce smaller, more direct prompts for Claude Code/local LLM agents.
+
+Acceptance Criteria:
+
+- Prompt includes exact known implementation gap when available
+- Prompt includes existing test command from CLAUDE.md
+- Prompt tells agent not to repeatedly reread unchanged files
+- Prompt tells agent to inspect first, then edit
+- Prompt limits scope to one small implementation step
+- Add/update tests