feat: initial project setup with implementation plan

- Add PLAN.md with 40-step checklist across 10 phases
- Add CLAUDE.md with project-specific instructions
- Set up nix flake with FastHTML/MonsterUI dependencies
- Create Python package skeleton (src/animaltrack)
- Vendor FastHTML and MonsterUI documentation
- Add Docker build configuration

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

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

CLAUDE.md

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+# AnimalTrack Project Instructions
+
+## Project Status
+Check `PLAN.md` for current progress. Each step has a checkbox to track completion.
+
+## Critical Workflow Rules
+
+### 1. Commit Frequently
+**ALWAYS commit after completing any step.** Don't let changes accumulate.
+
+### 2. Update Plan
+After completing work, update `PLAN.md`:
+- Check off completed items with `[x]`
+- Add commit hash if significant
+
+### 3. Run Tests
+```bash
+pytest tests/ -v
+```
+
+## Framework Documentation
+
+**ALWAYS consult docs before implementing UI.** Use vendored documentation.
+
+| Framework | Main Context | Examples |
+|-----------|-------------|----------|
+| FastHTML | `docs/vendor/fasthtml/llms-ctx.txt` | API refs in `docs/vendor/fasthtml/` |
+| MonsterUI | `docs/vendor/monsterui/llms.txt` | `docs/vendor/monsterui/examples/` |
+
+### Idiomatic Patterns
+- **Always check docs for the idiomatic way** before implementing anything with FastHTML/MonsterUI
+- MonsterUI components: `Card`, `Alert`, `Grid(cols_sm/md/lg)`, `DivFullySpaced`
+- Use `AlertT` enums for alerts, `TextPresets` for typography
+- Forms: Use MonsterUI form components, not raw HTML
+
+## Quick Reference
+
+### Database (APSW + FastLite)
+This project uses APSW (not standard sqlite3) via fastlite. Key patterns:
+```python
+from fastlite import database
+
+db = database('animaltrack.db')
+# db.execute() returns APSW cursor
+# Use db.t for table access
+```
+
+### Timestamps
+All timestamps are ms since Unix epoch, stored as INTEGER:
+```python
+import time
+ts_utc = int(time.time() * 1000)  # Current time in ms
+```
+
+### IDs
+All entity IDs are ULIDs (26 chars):
+```python
+from ulid import ULID
+id = str(ULID())  # "01ARZ3NDEKTSV4RRFFQ69G5FAV"
+```
+
+### Money
+Store all prices as integer cents. Display prices with 2 decimals, cost/egg with 3.
+
+## Project-Specific Rules
+
+### Event Sourcing
+- Every state change is an event
+- Events are immutable (edits create revisions, deletes create tombstones)
+- Projections are updated synchronously in the same transaction
+
+### Selection Context
+When handling animal selections:
+1. Client sends filter + resolved_ids + roster_hash
+2. Server re-resolves at ts_utc
+3. On mismatch: return 409 with diff, require `confirmed=true` to proceed
+
+### Feed Costing
+- Block FeedGiven if no FeedPurchased exists <= ts_utc
+- Store feed amounts in grams (INTEGER) for precision
+- Display as kg with 3 decimals
+
+## Refreshing Docs
+```bash
+# FastHTML
+curl -s https://www.fastht.ml/docs/llms-ctx.txt -o docs/vendor/fasthtml/llms-ctx.txt
+
+# MonsterUI
+curl -s https://raw.githubusercontent.com/AnswerDotAI/MonsterUI/refs/heads/main/docs/llms.txt -o docs/vendor/monsterui/llms.txt
+```
+
+## E2E Tests
+The spec defines 8 authoritative acceptance tests in §21. These are the source of truth for correct behavior. When in doubt, refer to the spec.
+
+Numeric comparisons on REAL values use tolerance `±0.001`.