# Add Status Reason to Task Display

## Goal
Show a human-readable explanation of *why* a task is in its current state, fix the pending review count to exclude terminal-state tasks, and replace approve/request-changes buttons with revoke buttons when a review is already submitted.

## Requirements

### R1. Add `status_reason` property to Task
Add a `status_reason` property on the `Task` dataclass that derives a human-readable explanation from the task's state, artifacts, and verdict status. For example:
- DONE → "Verdict: PASS"
- BLOCKED → "Verdict: FAIL — changes required before re-review"
- BUG_FIND (with IMPLEMENTATION.md) → "Implementation complete — awaiting bug finding"
- BACKLOG → "No artifacts yet — not started"

### R2. Expose `status_reason` in API responses
Include `status_reason` in the JSON response for both `/api/tasks` and `/api/task/{name}`.

### R3. Display status reason prominently
- Show `status_reason` below the status badge in the task detail panel
- Show `status_reason` on task cards for blocked/bug_find/adv_bug_find states

### R4. Fix pending review count
The pending review counter in the header currently counts all tasks without a review, including DONE tasks. Fix it to exclude terminal states (done, blocked) so only active tasks count toward pending.

### R5. Replace review buttons with revoke on submitted reviews
When a task already has an approved review, replace the approve button with "Revoke Approval". When changes are requested, replace with "Revoke Changes". Both send status="pending" to reset the review.

## Acceptance Criteria
- [ ] `status_reason` property works for all task states
- [ ] `/api/tasks` responses include `status_reason`
- [ ] Detail panel shows status reason below the status badge
- [ ] Task cards show status reason for blocked/bug_find/adv_bug_find tasks
- [ ] Pending review count excludes done/blocked tasks
- [ ] Approved tasks show "Revoke Approval" instead of "Approve"
- [ ] Backend accepts "pending" as a review status
- [ ] All tests pass

## Non-Goals
- Not changing the task state machine — revoking a review only resets the review metadata, not the task state
- Not adding buttons to change task state directly (e.g., send back to planning) — that's a larger feature