Drops the dead AI_ANALYZED status (a prior data migration already converted
existing rows; the choice was never removed from the model) and the
unreachable ACKNOWLEDGED status (is_recipient was hardcoded False so the
acknowledge button never rendered).
Changes:
- AppreciationStatus: DRAFT, ACTIVATED, SENT only. SENT is terminal.
- VALID_APPRECIATION_TRANSITIONS: DRAFT→ACTIVATED→SENT, SENT terminal.
- Removed the model.acknowledge() method.
- DRF viewset acknowledge action: returns 410 Gone (deprecated).
- UI appreciation_acknowledge view: redirects with deprecation message.
- Removed URL routes: appreciation_acknowledge, appreciation_send_dept_reminder.
- appreciation_send_dept_reminder status check no longer references ACKNOWLEDGED.
- appreciation_list stats + status filter + badge: dropped ai_analyzed/acknowledged.
- appreciation_detail status badge + sent banner: dropped acknowledged references.
- Migration 0010_drop_acknowledged_status: AlterField on status choices.
AI analysis still runs on activation and is stored in ai_analysis JSON; it
just no longer has its own status. Badges and leaderboard fire at SENT.
6 tests lock in the new lifecycle and removed URLs.
