fix: Resolve database migration failure on existing databases

Fixes critical issue where migration 002 indexes already existed in SCHEMA_SQL,
causing 'index already exists' errors on databases created before v1.0.0-rc.1.

Changes:
- Removed duplicate index definitions from SCHEMA_SQL (database.py)
- Enhanced migration system to detect and handle indexes properly
- Added comprehensive documentation of the fix

Version bumped to 1.0.0-rc.2 with full changelog entry.

Refs: docs/reports/2025-11-24-migration-fix-v1.0.0-rc.2.md

starpunk/database.py

@@ -55,10 +55,6 @@ CREATE TABLE IF NOT EXISTS tokens (
     revoked_at TIMESTAMP
 );
 
-CREATE INDEX IF NOT EXISTS idx_tokens_hash ON tokens(token_hash);
-CREATE INDEX IF NOT EXISTS idx_tokens_me ON tokens(me);
-CREATE INDEX IF NOT EXISTS idx_tokens_expires ON tokens(expires_at);
-
 -- Authorization codes for IndieAuth token exchange
 CREATE TABLE IF NOT EXISTS authorization_codes (
     id INTEGER PRIMARY KEY AUTOINCREMENT,