feat: convert workflow execute command to standalone skill

Move execute.md from commands/workflow/ to skills/workflow-execute/SKILL.md,
update all references in workflow-plan to use Skill(skill="workflow-execute")
instead of the old /workflow:execute command path.

.claude/skills/workflow-plan/phases/04-task-generation.md

@@ -0,0 +1,135 @@
+# Phase 4: Task Generation
+
+Generate implementation plan and task JSONs via action-planning-agent.
+
+## Objective
+
+- Generate IMPL_PLAN.md, task JSONs, and TODO_LIST.md
+- Present user with plan confirmation choices (verify / execute / review)
+- Route to Phase 5 (verify) if user selects verification
+
+## Relationship with Brainstorm Phase
+
+- If brainstorm role analyses exist ([role]/analysis.md files), they are incorporated as input
+- **User's original intent is ALWAYS primary**: New or refined user goals override brainstorm recommendations
+- **Role analysis.md files define "WHAT"**: Requirements, design specs, role-specific insights
+- **IMPL_PLAN.md defines "HOW"**: Executable task breakdown, dependencies, implementation sequence
+- Task generation translates high-level role analyses into concrete, actionable work items
+- **Intent priority**: Current user prompt > role analysis.md files > guidance-specification.md
+
+## Execution
+
+### Step 4.1: Execute Task Generation
+
+```javascript
+Skill(skill="workflow:tools:task-generate-agent", args="--session [sessionId]")
+```
+
+**CLI Execution Note**: CLI tool usage is now determined semantically by action-planning-agent based on user's task description. If user specifies "use Codex/Gemini/Qwen for X", CLI tool usage is controlled by `meta.execution_config.method` per task, not by `command` fields in implementation steps.
+
+**Input**:
+- `sessionId` from Phase 1
+- **planning-notes.md**: Consolidated constraints from all phases (Phase 1-3)
+  - Path: `.workflow/active/[sessionId]/planning-notes.md`
+  - Contains: User intent, context findings, conflict decisions, consolidated constraints
+  - **Purpose**: Provides structured, minimal context summary to action-planning-agent
+
+**Validation**:
+- `.workflow/active/[sessionId]/plan.json` exists (structured plan overview)
+- `.workflow/active/[sessionId]/IMPL_PLAN.md` exists
+- `.workflow/active/[sessionId]/.task/IMPL-*.json` exists (at least one)
+- `.workflow/active/[sessionId]/TODO_LIST.md` exists
+
+### TodoWrite Update (Phase 4 Skill executed - agent task attached)
+
+```json
+[
+  {"content": "Phase 1: Session Discovery", "status": "completed", "activeForm": "Executing session discovery"},
+  {"content": "Phase 2: Context Gathering", "status": "completed", "activeForm": "Executing context gathering"},
+  {"content": "Phase 4: Task Generation", "status": "in_progress", "activeForm": "Executing task generation"}
+]
+```
+
+**Note**: Single agent task attached. Agent autonomously completes discovery, planning, and output generation internally.
+
+### TodoWrite Update (Phase 4 completed)
+
+```json
+[
+  {"content": "Phase 1: Session Discovery", "status": "completed", "activeForm": "Executing session discovery"},
+  {"content": "Phase 2: Context Gathering", "status": "completed", "activeForm": "Executing context gathering"},
+  {"content": "Phase 4: Task Generation", "status": "completed", "activeForm": "Executing task generation"}
+]
+```
+
+**Note**: Agent task completed. No collapse needed (single task).
+
+### Step 4.2: Plan Confirmation (User Decision Gate)
+
+After Phase 4 completes, present user with action choices:
+
+```javascript
+console.log(`
+Planning complete for session: ${sessionId}
+Tasks generated: ${taskCount}
+Plan: .workflow/active/${sessionId}/IMPL_PLAN.md
+`);
+
+// Ask user for next action
+const userChoice = AskUserQuestion({
+  questions: [{
+    question: "Planning complete. What would you like to do next?",
+    header: "Next Action",
+    multiSelect: false,
+    options: [
+      {
+        label: "Verify Plan Quality (Recommended)",
+        description: "Run quality verification to catch issues before execution. Checks plan structure, task dependencies, and completeness."
+      },
+      {
+        label: "Start Execution",
+        description: "Begin implementing tasks immediately. Use this if you've already reviewed the plan or want to start quickly."
+      },
+      {
+        label: "Review Status Only",
+        description: "View task breakdown and session status without taking further action. You can decide what to do next manually."
+      }
+    ]
+  }]
+});
+
+// Execute based on user choice
+if (userChoice.answers["Next Action"] === "Verify Plan Quality (Recommended)") {
+  console.log("\nStarting plan verification...\n");
+  // Route to Phase 5 (plan-verify) within this skill
+  // Orchestrator reads phases/05-plan-verify.md and executes
+} else if (userChoice.answers["Next Action"] === "Start Execution") {
+  console.log("\nStarting task execution...\n");
+  Skill(skill="workflow-execute", args="--session " + sessionId);
+} else if (userChoice.answers["Next Action"] === "Review Status Only") {
+  console.log("\nDisplaying session status...\n");
+  Skill(skill="workflow:status", args="--session " + sessionId);
+}
+```
+
+**Auto Mode (--yes)**: Auto-select "Verify Plan Quality", then auto-continue to execute if quality gate is PROCEED.
+
+**Return to Orchestrator**: Based on user's choice:
+- **Verify** → Orchestrator reads phases/05-plan-verify.md and executes Phase 5 in-process
+- **Execute** → Skill(skill="workflow-execute")
+- **Review** → Route to /workflow:status
+
+## Output
+
+- **File**: `IMPL_PLAN.md` (implementation plan)
+- **File**: `IMPL-*.json` (task JSON files)
+- **File**: `TODO_LIST.md` (task list)
+- **File**: `plan.json` (structured plan overview)
+- **TodoWrite**: Mark Phase 4 completed
+
+## Next Phase (Conditional)
+
+Based on user's plan confirmation choice:
+- If "Verify" → [Phase 5: Plan Verification](05-plan-verify.md)
+- If "Execute" → Skill(skill="workflow-execute")
+- If "Review" → External: /workflow:status