feat: implement Animal Detail page with timeline (Step 8.3)

Add GET /animals/{animal_id} route to display individual animal details:
- Header summary with species, location, status, tags
- Event timeline showing all events affecting the animal (newest first)
- Quick actions card (Move functional, others disabled for now)
- Merge info alert for animals that have been merged

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

PLAN.md

@@ -326,15 +326,15 @@ Check off items as completed. Each phase builds on the previous.
 - [x] **Commit checkpoint**
 
 ### Step 8.3: Animal Detail Drawer
-- [ ] Create `web/routes/animals.py`:
-  - [ ] GET /animals/{animal_id}
-- [ ] Create `web/templates/animal_detail.py`:
-  - [ ] Header summary
-  - [ ] Timeline (newest first)
-  - [ ] Quick actions
-- [ ] Create `repositories/animal_timeline.py`
-- [ ] Write tests: detail renders, timeline shows events, merge info shown
-- [ ] **Commit checkpoint**
+- [x] Create `web/routes/animals.py`:
+  - [x] GET /animals/{animal_id}
+- [x] Create `web/templates/animal_detail.py`:
+  - [x] Header summary
+  - [x] Timeline (newest first)
+  - [x] Quick actions
+- [x] Create `repositories/animal_timeline.py`
+- [x] Write tests: detail renders, timeline shows events, merge info shown
+- [x] **Commit checkpoint**
 
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