docs: add hooks guide, expand planner agent, add Django example

- Add hooks/README.md: comprehensive hook documentation with input schema,
  customization guide, 4 ready-to-use hook recipes, and cross-platform notes
- Expand planner agent with full worked example (Stripe subscriptions plan)
  and sizing/phasing guidance (119 → 212 lines)
- Add Django REST API example config (DRF + Celery + pytest + Factory Boy)
- Update README directory tree with new files

agents/planner.md

@@ -98,6 +98,85 @@ Create detailed steps with:
 6. **Think Incrementally**: Each step should be verifiable
 7. **Document Decisions**: Explain why, not just what
 
+## Worked Example: Adding Stripe Subscriptions
+
+Here is a complete plan showing the level of detail expected:
+
+```markdown
+# Implementation Plan: Stripe Subscription Billing
+
+## Overview
+Add subscription billing with free/pro/enterprise tiers. Users upgrade via
+Stripe Checkout, and webhook events keep subscription status in sync.
+
+## Requirements
+- Three tiers: Free (default), Pro ($29/mo), Enterprise ($99/mo)
+- Stripe Checkout for payment flow
+- Webhook handler for subscription lifecycle events
+- Feature gating based on subscription tier
+
+## Architecture Changes
+- New table: `subscriptions` (user_id, stripe_customer_id, stripe_subscription_id, status, tier)
+- New API route: `app/api/checkout/route.ts` — creates Stripe Checkout session
+- New API route: `app/api/webhooks/stripe/route.ts` — handles Stripe events
+- New middleware: check subscription tier for gated features
+- New component: `PricingTable` — displays tiers with upgrade buttons
+
+## Implementation Steps
+
+### Phase 1: Database & Backend (2 files)
+1. **Create subscription migration** (File: supabase/migrations/004_subscriptions.sql)
+   - Action: CREATE TABLE subscriptions with RLS policies
+   - Why: Store billing state server-side, never trust client
+   - Dependencies: None
+   - Risk: Low
+
+2. **Create Stripe webhook handler** (File: src/app/api/webhooks/stripe/route.ts)
+   - Action: Handle checkout.session.completed, customer.subscription.updated,
+     customer.subscription.deleted events
+   - Why: Keep subscription status in sync with Stripe
+   - Dependencies: Step 1 (needs subscriptions table)
+   - Risk: High — webhook signature verification is critical
+
+### Phase 2: Checkout Flow (2 files)
+3. **Create checkout API route** (File: src/app/api/checkout/route.ts)
+   - Action: Create Stripe Checkout session with price_id and success/cancel URLs
+   - Why: Server-side session creation prevents price tampering
+   - Dependencies: Step 1
+   - Risk: Medium — must validate user is authenticated
+
+4. **Build pricing page** (File: src/components/PricingTable.tsx)
+   - Action: Display three tiers with feature comparison and upgrade buttons
+   - Why: User-facing upgrade flow
+   - Dependencies: Step 3
+   - Risk: Low
+
+### Phase 3: Feature Gating (1 file)
+5. **Add tier-based middleware** (File: src/middleware.ts)
+   - Action: Check subscription tier on protected routes, redirect free users
+   - Why: Enforce tier limits server-side
+   - Dependencies: Steps 1-2 (needs subscription data)
+   - Risk: Medium — must handle edge cases (expired, past_due)
+
+## Testing Strategy
+- Unit tests: Webhook event parsing, tier checking logic
+- Integration tests: Checkout session creation, webhook processing
+- E2E tests: Full upgrade flow (Stripe test mode)
+
+## Risks & Mitigations
+- **Risk**: Webhook events arrive out of order
+  - Mitigation: Use event timestamps, idempotent updates
+- **Risk**: User upgrades but webhook fails
+  - Mitigation: Poll Stripe as fallback, show "processing" state
+
+## Success Criteria
+- [ ] User can upgrade from Free to Pro via Stripe Checkout
+- [ ] Webhook correctly syncs subscription status
+- [ ] Free users cannot access Pro features
+- [ ] Downgrade/cancellation works correctly
+- [ ] All tests pass with 80%+ coverage
+```
+
 ## When Planning Refactors
 
 1. Identify code smells and technical debt
@@ -106,6 +185,17 @@ Create detailed steps with:
 4. Create backwards-compatible changes when possible
 5. Plan for gradual migration if needed
 
+## Sizing and Phasing
+
+When the feature is large, break it into independently deliverable phases:
+
+- **Phase 1**: Minimum viable — smallest slice that provides value
+- **Phase 2**: Core experience — complete happy path
+- **Phase 3**: Edge cases — error handling, edge cases, polish
+- **Phase 4**: Optimization — performance, monitoring, analytics
+
+Each phase should be mergeable independently. Avoid plans that require all phases to complete before anything works.
+
 ## Red Flags to Check
 
 - Large functions (>50 lines)
@@ -115,5 +205,8 @@ Create detailed steps with:
 - Hardcoded values
 - Missing tests
 - Performance bottlenecks
+- Plans with no testing strategy
+- Steps without clear file paths
+- Phases that cannot be delivered independently
 
 **Remember**: A great plan is specific, actionable, and considers both the happy path and edge cases. The best plans enable confident, incremental implementation.