fix: persist toggled databases on the DATABASE_URL connection across reloads

[matej21]

Follow-up to #16.

Problem

After #16 stopped the Connection not found error when toggling extra databases on a server-managed (DATABASE_URL) connection, the toggle worked in-session but the activated databases disappeared on page reload.

Each WebSocket gets a fresh in-memory app DB, and the env connection is recreated from DATABASE_URL on every session with no memory of what was activated — so nothing durable held the active-database list.

Fix

Remember the env connection's active databases in a process-scoped Set in backend-web/session.ts:

• seed the connection config from it on session creation, so the existing fire-and-forget auto-connect reconnects those databases;
• update it by wrapping the databases.activate / databases.deactivate handlers, mirroring the existing connections.list wrap.

Scope: this only affects the single shared DATABASE_URL connection (web mode). It is process-scoped — shared across sessions of that one connection and reset on server restart (the env connection is ephemeral by nature).

Verification

• bun run typecheck ✅, biome lint ✅, bun test (web-session / ephemeral-session / env-connection: 45 pass) ✅
• Browser against a real Postgres: activate a 2nd database → reload → still present; deactivate → reload → gone.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NxZYcCWNSKYkMqT3KYdwTB