feat: complete v0.3.0 database migration and configuration

Final phase of v0.3.0 implementation - all core features complete.

Price Tools Migration:
- Update get_open_prices() to query price_data table
- Update get_yesterday_open_and_close_price() to query database
- Remove merged.jsonl file I/O (replaced with SQLite queries)
- Maintain backward-compatible function signatures
- Add db_path parameter (default: data/jobs.db)

Configuration:
- Add AUTO_DOWNLOAD_PRICE_DATA to .env.example (default: true)
- Add MAX_SIMULATION_DAYS to .env.example (default: 30)
- Document new configuration options

Documentation:
- Comprehensive CHANGELOG updates for v0.3.0
- Document all breaking changes (API format, data storage, config)
- Document new features (on-demand downloads, date ranges, database)
- Document migration path (scripts/migrate_price_data.py)
- Clear upgrade instructions

Breaking Changes (v0.3.0):
1. API request format: date_range -> start_date/end_date
2. Data storage: merged.jsonl -> price_data table
3. Config variables: removed RUNTIME_ENV_PATH, MCP ports, WEB_HTTP_PORT
4. Added AUTO_DOWNLOAD_PRICE_DATA, MAX_SIMULATION_DAYS

Migration Steps:
1. Run: python scripts/migrate_price_data.py
2. Update API clients to use new date format
3. Update .env with new variables
4. Remove old config variables

Status: v0.3.0 implementation complete
Ready for: Testing, deployment, and release

.env.example

@@ -24,6 +24,16 @@ API_PORT=8080
 # Agent Configuration
 AGENT_MAX_STEP=30
 
+# Simulation Configuration
+# Maximum number of days allowed in a single simulation range
+# Prevents accidentally requesting very large date ranges
+MAX_SIMULATION_DAYS=30
+
+# Price Data Configuration
+# Automatically download missing price data from Alpha Vantage when needed
+# If disabled, all price data must be pre-populated in the database
+AUTO_DOWNLOAD_PRICE_DATA=true
+
 # Data Volume Configuration
 # Base directory for all persistent data (will contain data/, logs/, configs/ subdirectories)
 # Use relative paths (./volumes) or absolute paths (/home/user/ai-trader-volumes)