Add seed script with 7 trees, markdown rendering, and dark mode docs

- Add comprehensive seed script with 7 troubleshooting decision trees
  - Tier 1: Password Reset, Outlook/Email, VPN, Printer Problems
  - Tier 2: Slow Computer, Network Connectivity
  - Tier 3: File Share Access Problems
- Add markdown rendering with react-markdown package
  - MarkdownContent component for session player and node editor
  - Preview toggle in description fields
- Update documentation to reflect dark mode is complete
- Update all progress tracking docs with recent changes

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

LESSONS-LEARNED.md

@@ -6,6 +6,69 @@
 
 ---
 
+## Environment Setup (New Machine)
+
+### Database Name Mismatch After Fresh Clone
+**Problem:** After cloning the repo and running `docker-compose up -d`, Alembic migrations fail with `database "decision_tree" does not exist`.
+
+**Cause:** The `.env` file contains the old database name (`decision_tree`) but `docker-compose.yml` creates a database called `apoklisis`.
+
+**Solution:** Update `.env` to use the correct database name:
+```
+DATABASE_URL=postgresql+asyncpg://postgres:postgres@localhost:5432/apoklisis
+DATABASE_URL_SYNC=postgresql://postgres:postgres@localhost:5432/apoklisis
+```
+
+**Files affected:** `backend/.env`
+
+---
+
+### Missing @/lib/utils (cn function)
+**Problem:** Frontend fails to compile with error: `Failed to resolve import "@/lib/utils" from "src/pages/SessionDetailPage.tsx". Does the file exist?`
+
+**Cause:** The `src/lib/utils.ts` file wasn't committed to the repo or was missed during setup. This file provides the `cn()` utility function used for combining Tailwind classes.
+
+**Solution:** Create `frontend/src/lib/utils.ts`:
+```typescript
+import { type ClassValue, clsx } from 'clsx'
+import { twMerge } from 'tailwind-merge'
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs))
+}
+```
+
+**Dependencies required:** `clsx` and `tailwind-merge` (already in package.json)
+
+**Files affected:** `frontend/src/lib/utils.ts`
+
+---
+
+### pip install in venv doesn't need --break-system-packages
+**Problem:** Confusion about whether to use `--break-system-packages` flag.
+
+**Clarification:** The `--break-system-packages` flag is only needed when installing packages **outside** of a virtual environment. When your venv is active (you see `(venv)` prefix), you don't need this flag.
+
+---
+
+### New Machine Setup Checklist
+When setting up development on a new machine:
+
+1. **Clone repo:** `git clone <repo-url>`
+2. **Start Docker Desktop**
+3. **Start database:** `cd backend && docker-compose up -d`
+4. **Fix .env database name** if it says `decision_tree` → change to `apoklisis`
+5. **Create venv:** `python -m venv venv`
+6. **Activate venv:** `.\venv\Scripts\Activate`
+7. **Install backend deps:** `pip install -r requirements.txt`
+8. **Run migrations:** `alembic upgrade head`
+9. **Start backend:** `uvicorn app.main:app --reload`
+10. **Install frontend deps:** `cd ../frontend && npm install`
+11. **Create lib/utils.ts** if missing (see above)
+12. **Start frontend:** `npm run dev`
+
+---
+
 ## Python / Backend
 
 ### DateTime Timezone Handling ⚠️ CRITICAL
@@ -428,6 +491,40 @@ pytest
 
 ---
 
+## Seed Scripts
+
+### httpx Not Installed
+**Problem:** Running `python -m scripts.seed_trees` fails with `ModuleNotFoundError: No module named 'httpx'`
+
+**Cause:** The seed script uses `httpx` for async HTTP requests, which isn't in the base requirements.
+
+**Solution:** Install httpx before running seed scripts:
+```powershell
+pip install httpx
+```
+
+---
+
+### Email Validation Rejects .local Domains
+**Problem:** Seed script fails with email validation error when using `.local` domain for seed user email.
+
+**Error:** `value is not a valid email address: The part after the @-sign is a special-use or reserved name that cannot be used with email.`
+
+**Cause:** The `email-validator` library (used by Pydantic) correctly rejects `.local` as it's a reserved TLD per RFC 6761.
+
+**Solution:** Use a standard domain like `example.com` for seed/test users:
+```python
+# BAD
+"email": "seed.admin@apoklisis.local"
+
+# GOOD
+"email": "seed.admin@example.com"
+```
+
+**Files affected:** `backend/scripts/seed_trees.py`, any test fixtures with email addresses
+
+---
+
 ## Adding New Lessons
 
 When you encounter and fix a bug, add it here with: