feat(miner-plan): discover→manage plan-template library extending the MCP plan-DAG shape

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The fixed miner lifecycle is discover → analyze → plan → prepare → create → manage → repeat. Rather than every miner inventing its own step graph from scratch, provide a library of reusable plan TEMPLATES in the exact stateless DAG shape the existing MCP tools already speak: gittensory_build_plan / gittensory_plan_status / gittensory_record_step_result (src/mcp/server.ts:1421-1434), whose steps carry id/title/actionClass/dependsOn/maxAttempts (see rawPlanStepSchema at src/mcp/server.ts:324). This is pure data + a small builder function — no new state machine, since gittensory_build_plan already normalizes raw steps into the validated DAG.

Deliverables

• packages/gittensory-engine/src/plan-templates.ts exporting one template function per lifecycle stage transition, e.g. analyzeToplanTemplate(issueContext) returning RawPlanStep[] in EXACTLY the shape gittensory_build_plan's buildPlanShape expects ({ id, title, actionClass?, dependsOn?, maxAttempts? })
• At minimum: an "analyze" template (feasibility check → RAG retrieval → prompt-packet build) and a "prepare" template (branch creation → coding-agent invocation placeholder step → local test run)
• Each template's steps use dependsOn to encode the real ordering (e.g. prompt-packet build depends on both feasibility-check and RAG-retrieval steps completing)
• Unit tests asserting each template's output round-trips cleanly through the ACTUAL rawPlanStepSchema zod shape (import it, don't hand-roll a copy) so the templates never drift from what gittensory_build_plan accepts
• No actuation anywhere — templates only describe steps; they don't run anything

References

• src/mcp/server.ts:1421 (gittensory_build_plan tool registration + description)
• src/mcp/server.ts:324 (rawPlanStepSchema — the EXACT step shape templates must produce)
• src/mcp/server.ts:333 (planStepSchema — the normalized shape build_plan returns, showing status/attempts get added)
• src/mcp/server.ts:321 (module comment: "feat(agent): multi-step action DAG executor #783 multi-step plan DAG — stateless: pass the plan back each call")

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JSO-2414