Extract shared WarehouseResource from raw psycopg2 usage

[24c02]

Problem

Every asset that touches postgres does its own os.getenv("WAREHOUSE_COOLIFY_URL") + psycopg2.connect(). There are 10+ files doing this independently with no shared connection management.

Proposal

Create a WarehouseResource(ConfigurableResource) that:

• Takes connection_url via EnvVar("WAREHOUSE_COOLIFY_URL")
• Exposes a get_connection() context manager
• Gets wired into Definitions once and injected via type annotations

Then migrate existing assets to use it instead of raw psycopg2.

Files to migrate

• defs/airtable_raw_all_bases/definitions.py
• defs/airtable_audit_logs/definitions.py
• defs/loops_campaign_and_metrics_export/definitions.py
• defs/ysws_programs_sync/definitions.py
• defs/unified_ysws_db/definitions.py
• defs/agh_fulfillment_zenventory/definitions.py
• defs/zenventory_inventory_airtable_sync/definitions.py
• defs/slack_users_sync/definitions.py
• defs/slack/definitions.py
• defs/ducklake/definitions.py