fix: resolve migration 0005 duplicate constraint failure (#97)

**Problem:**
- Users upgrading to v3.7.2 encountered database migration failures
- Migration 0005 tried to add unique index without handling existing duplicates
- Hybrid initialization (manual SQL + Drizzle) caused schema inconsistencies
- Error: "UNIQUE constraint failed: repositories.user_id, repositories.full_name"

**Solution:**

1. **Fixed Migration 0005:**
   - Added deduplication step before creating unique index
   - Removes duplicate (user_id, full_name) entries, keeping most recent
   - Safely creates unique constraint after cleanup

2. **Removed Hybrid Database Initialization:**
   - Eliminated 154 lines of manual SQL from docker-entrypoint.sh
   - Now uses Drizzle exclusively for schema management
   - Single source of truth prevents schema drift
   - Migrations run automatically via src/lib/db/index.ts

**Testing:**
- ✅ Fresh database initialization works
- ✅ Duplicate deduplication verified
- ✅ Unique constraint properly enforced
- ✅ All 6 migrations apply cleanly

**Changes:**
- docker-entrypoint.sh: Removed manual table creation SQL
- drizzle/0005_polite_preak.sql: Added deduplication before index creation

Fixes #97

drizzle/0005_polite_preak.sql

@@ -1 +1,11 @@
-CREATE UNIQUE INDEX `uniq_repositories_user_full_name` ON `repositories` (`user_id`,`full_name`);
+-- Step 1: Remove duplicate repositories, keeping the most recently updated one
+-- This handles cases where users have duplicate entries from before the unique constraint
+DELETE FROM repositories
+WHERE rowid NOT IN (
+  SELECT MAX(rowid)
+  FROM repositories
+  GROUP BY user_id, full_name
+);
+--> statement-breakpoint
+-- Step 2: Now create the unique index safely
+CREATE UNIQUE INDEX uniq_repositories_user_full_name ON repositories (user_id, full_name);