feat: public_port for managed databases — opt-in 0.0.0.0 bind

Managed databases have always published their port on 127.0.0.1 only.
public_port opts into binding on all interfaces so the database is
reachable off-host. Toggling via PUT recreates the container — the
named data volume survives.

- create accepts public_port; PUT /databases/{id} toggles it
- external rows reject the flag (no container exists)
- CLI: databases create --public, databases update --public/--public=false
- MCP: databases_update tool; UI: create checkbox + per-row toggle

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/sqlc/schema.sql

@@ -146,6 +146,7 @@ CREATE TABLE database_services (
     external_username VARCHAR(255),
     external_password TEXT NOT NULL DEFAULT '',
     external_ssl BOOLEAN NOT NULL DEFAULT false,
+    public_port BOOLEAN NOT NULL DEFAULT false,
     created_at TIMESTAMP WITH TIME ZONE DEFAULT NOW(),
     updated_at TIMESTAMP WITH TIME ZONE DEFAULT NOW()
 );