feat: [Phase 2] Connection manager + 10 Node.js DB drivers

[anandgupta42]

Phase 2: Connection Manager + DB Drivers

Parent: #214
Depends on: Phase 1

What

Replace the Python ConnectionRegistry, 10 warehouse connectors, credential store, SSH tunneling, and Docker discovery with TypeScript equivalents using native Node.js drivers.

Sub-tasks

• native/connections/registry.ts — reads connections.json, env vars, project config
• native/connections/credential-store.ts — 3-tier: keytar → AES-256 → env vars (no plaintext)
• native/connections/ssh-tunnel.ts — ssh2 with SIGINT/exit cleanup
• native/connections/docker-discovery.ts — dockerode
• native/connections/dbt-profiles.ts — YAML + Jinja {{ env_var() }} regex
• 10 driver files: snowflake, bigquery, postgres, databricks, redshift, mysql, sqlserver, oracle, duckdb, sqlite
• Lazy driver loading via dynamic import()
• Register 14 dispatcher methods
• connections.json backward compatibility test
• Integration tests against local PostgreSQL + DuckDB

Drivers

Driver	Package	Pure JS?
snowflake	snowflake-sdk	Yes
bigquery	@google-cloud/bigquery	Yes
postgres	pg	Yes
databricks	@databricks/sql / REST	Yes
redshift	pg	Yes
mysql	mysql2	Yes
sqlserver	mssql/tedious	Yes
oracle	oracledb thin	Yes (12.1+)
duckdb	@duckdb/node-api	optionalDep
sqlite	better-sqlite3	optionalDep

[anandgupta42]

Completed in PR #221.