feat: r0 coordinator tooling for orchestrator protocol

Implements the manual coordinator workflow for multi-session agent
orchestration. Agents stop after one milestone (confirmed limitation);
these tools let the human coordinator check status, generate continuation
prompts, and chain sessions together.

New:
- tools/orchestrator/ — 5 scripts + shared library (_lib.sh)
  - mission-init.sh: initialize mission with milestones and state files
  - mission-status.sh: dashboard showing milestones, tasks, sessions
  - session-status.sh: check if agent is running/stale/dead
  - continue-prompt.sh: generate paste-ready continuation prompt
  - session-resume.sh: crash recovery with dirty state detection
- guides/ORCHESTRATOR-PROTOCOL.md: agent-facing mission lifecycle guide
- templates/docs/: mission manifest, scratchpad, continuation templates
- templates/repo/.mosaic/orchestrator/mission.json: state file template

Modified:
- bin/mosaic: add 'coord' subcommand + resume advisory on launch
- AGENTS.md: conditional loading for protocol guide + rule 37
- bin/mosaic-doctor: checks for new coordinator files
- session hooks: mission detection on start, cleanup on end

Usage: mosaic coord init|mission|status|continue|resume

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/docs/mission-scratchpad.md.template

@@ -0,0 +1,27 @@
+# Mission Scratchpad — ${MISSION_NAME}
+
+> Append-only log. NEVER delete entries. NEVER overwrite sections.
+> This is the orchestrator's working memory across sessions.
+
+## Original Mission Prompt
+
+```
+${MISSION_PROMPT}
+```
+
+## Planning Decisions
+
+<!-- Record key decisions made during planning. Format: decision + rationale. -->
+
+## Session Log
+
+| Session | Date | Milestone | Tasks Done | Outcome |
+|---------|------|-----------|------------|---------|
+
+## Open Questions
+
+<!-- Unresolved items that need human input or cross-session investigation. -->
+
+## Corrections
+
+<!-- Record any corrections to earlier decisions or assumptions. -->