feat: add templates for architecture documents, epics, product briefs, and requirements PRD

- Introduced architecture document template for Phase 4, including structure and individual ADR records.
- Added epics & stories template for Phase 5, detailing epic breakdown and dependencies.
- Created product brief template for Phase 2, summarizing product vision, problem statement, and target users.
- Developed requirements PRD template for Phase 3, outlining functional and non-functional requirements with traceability.
- Implemented spec command for project spec management with subcommands for loading, listing, rebuilding, and initializing specs.

.claude/skills/workflow-lite-plan/phases/01-lite-plan.md

@@ -714,13 +714,55 @@ executionContext = {
 }
 ```
 
-**Step 5.2: Handoff**
+**Step 5.2: Serialize & Agent Handoff**
+
+> **Why agent handoff**: Phase 1 history consumes significant context. Direct `Read("phases/02-lite-execute.md")` in the same context risks compact compressing Phase 2 instructions mid-execution. Spawning a fresh agent gives Phase 2 a clean context window.
 
 ```javascript
-// Direct phase handoff: Read and execute Phase 2 (lite-execute) with in-memory context
-// No Skill routing needed - executionContext is already set in Step 5.1
-Read("phases/02-lite-execute.md")
-// Execute Phase 2 with executionContext (Mode 1: In-Memory Plan)
+// Pre-populate _loadedTasks so serialized context is self-contained
+executionContext.planObject._loadedTasks = (executionContext.planObject.task_ids || []).map(id =>
+  JSON.parse(Read(`${sessionFolder}/.task/${id}.json`))
+)
+
+// Save executionContext to file for agent handoff
+Write(`${sessionFolder}/execution-context.json`, JSON.stringify(executionContext, null, 2))
+
+// Resolve absolute path to Phase 2 instructions
+const phaseFile = Bash(`cd "${Bash('pwd').trim()}/.claude/skills/workflow-lite-plan/phases" && pwd`).trim()
+  + '/02-lite-execute.md'
+
+// Agent handoff: fresh context prevents compact from losing Phase 2 instructions
+Task(
+  subagent_type="universal-executor",
+  run_in_background=false,
+  description=`Execute: ${taskSlug}`,
+  prompt=`
+Execute implementation plan following lite-execute protocol.
+
+## Phase Instructions (MUST read first)
+Read and follow: ${phaseFile}
+
+## Execution Context (Mode 1: In-Memory Plan)
+Read and parse as JSON: ${sessionFolder}/execution-context.json
+This is the executionContext variable referenced throughout Phase 2.
+The planObject._loadedTasks array is pre-populated — getTasks(planObject) works directly.
+
+## Key References
+- Session ID: ${sessionId}
+- Session folder: ${sessionFolder}
+- Plan: ${sessionFolder}/plan.json
+- Task files: ${sessionFolder}/.task/TASK-*.json
+- Original task: ${task_description}
+
+## Execution Steps
+1. Read phase instructions file (full protocol)
+2. Read execution-context.json → parse as executionContext
+3. Follow Phase 2 Mode 1 (In-Memory Plan) — executionContext exists, skip user selection
+4. Execute all tasks (Step 1-4 in Phase 2)
+5. Run code review if codeReviewTool ≠ "Skip" (Step 5)
+6. Run auto-sync (Step 6)
+`
+)
 ```
 
 ## Session Folder Structure