fix: Complete rewrite of progress tracking system (v1.0.9)

The /ab:build command was executing tasks but not tracking progress.
This rewrite enforces dual progress tracking in BOTH status.json AND plan.md.

Key changes:

build.md - Complete restructure:
- Step-by-step execution workflow (like migrate.md)
- Step 4d MANDATORY: Update both status.json and plan.md
- User confirmation required between tasks
- Visual Progress Tracker table in plan template

planner.md - New plan template:
- Progress Tracker table at top with ⬜/✅ indicators
- Each task has `- **Status**: ⬜ Pending` field
- Status header shows overall progress

coder.md - Dual file updates:
- 5a: Update status.json (currentTask, tasksCompleted, history)
- 5b: Update plan.md Progress Tracker (⬜ Pending → ✅ Done)

Benefits:
- Visual progress in plan.md (human readable)
- JSON progress in status.json (programmatic)
- Redundancy ensures progress is never lost
- Team can see exactly which tasks are complete

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugin/agents/coder.md

@@ -68,13 +68,62 @@ After coding:
 - Verify changes match completion criteria
 - Ensure no unintended side effects
 
-### 5. Report Changes
+### 5. Update Progress (MANDATORY)
+
+**After completing the task, you MUST update BOTH files:**
+
+#### 5a. Update status.json
+
+Read and update `.auto-build/specs/{feature-name}/status.json`:
+```json
+{
+  "status": "IMPLEMENTING",
+  "currentTask": {N+1},
+  "tasksCompleted": {N},
+  "totalTasks": {TOTAL},
+  "updated": "{ISO timestamp}",
+  "history": [
+    ...existing...,
+    {"status": "IMPLEMENTING", "at": "{timestamp}", "task": {N}, "title": "{title}", "completed": true}
+  ]
+}
+```
+
+#### 5b. Update plan.md Progress Tracker
+
+Edit `.auto-build/specs/{feature-name}/plan.md` to mark task complete:
+
+1. In the Progress Tracker table, change:
+   ```
+   | {N} | {Task title} | ⬜ Pending | |
+   ```
+   to:
+   ```
+   | {N} | {Task title} | ✅ Done | {timestamp} |
+   ```
+
+2. In the task section, change:
+   ```
+   - **Status**: ⬜ Pending
+   ```
+   to:
+   ```
+   - **Status**: ✅ Done ({timestamp})
+   ```
+
+**Both updates are MANDATORY. Skipping them breaks team collaboration and progress tracking.**
+
+### 6. Report Changes
 
 Provide a summary:
 
 ```markdown
 ## Task Completed: [Task Title]
 
+### Progress Updated
+- status.json updated: currentTask = {N+1}
+- History entry added for task {N}
+
 ### Changes Made
 
 #### `path/to/file1.ts`