fix: studio crashes when user lacks privileges on some schemas

[xiekw2010]

Summary

• Problem: Drizzle Studio crashes with Identity realtime.subscription.id columns missing metadata: null when the database user only has access to specific schemas (e.g. multi-tenant setups with schema-level isolation, or Supabase with restricted roles). The Studio frontend introspects all visible schemas including ones the user cannot fully read, causing a fatal error.

• Fix 1 — Graceful handling of missing metadata: Changed throw to console.warn + continue in introspect functions (postgres/introspect.ts, postgres/aws-introspect.ts, cockroach/introspect.ts) when identity or generated column metadata is null, so a single inaccessible column doesn't crash the entire introspection.

• Fix 2 — Studio respects schemaFilter: Passed the schemaFilter config from drizzle.config.ts through to the Studio proxy server. The proxy now filters pg_namespace query results so the Studio frontend only sees schemas the user has configured, preventing it from attempting to introspect schemas the user lacks privileges on.

How to reproduce

1. Connect to a PostgreSQL database where the user only has access to a specific schema (not the full database)
2. The database has other schemas (e.g. Supabase's realtime, auth) with identity columns
3. Configure schemaFilter in drizzle.config.ts
4. Run drizzle-kit studio
5. Studio crashes with "Identity ... columns missing metadata: null"

Test plan

• Verified locally with a Supabase PostgreSQL instance where the user only has access to a single schema (app_play4supabase_dev)
• Studio now loads correctly and shows only the filtered schema's tables
• schemaFilter is correctly read from drizzle.config.ts and passed through to the Studio proxy
• Other drizzle-kit commands (push, generate) are not affected

Related issues: #2946, #4042

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