feat: Add initial PostgreSQL best practices rules (#1)

* Add 30 PostgreSQL best practices rules

Rules organized in 8 categories:
- Query Performance (5): indexes, partial indexes, composite, covering, types
- Connection Management (4): pooling, limits, idle timeout, prepared statements
- Schema Design (4): data types, primary keys, foreign key indexes, partitioning
- Concurrency & Locking (4): short transactions, SKIP LOCKED, advisory, deadlocks
- Security (3): RLS basics, RLS performance, privileges
- Data Access Patterns (4): N+1 queries, pagination, upsert, batch inserts
- Monitoring (3): EXPLAIN ANALYZE, pg_stat_statements, VACUUM/ANALYZE
- Advanced Features (3): JSONB indexing, full-text search, CTE materialization

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Update skills/postgresql-best-practices/rules/schema-primary-keys.md

Co-authored-by: samrose <samuel.rose@gmail.com>

* Update skills/postgresql-best-practices/rules/lock-deadlock-prevention.md

Co-authored-by: samrose <samuel.rose@gmail.com>

* resolve merge conflicts from postgres team suggestions

* Delete GETTING_STARTED.md

* Restore all 30 rule files that were lost during rebase

* update agents.md

* remove postgres 11 mention to advanced cte optimization

* update agents.md

* replace advanced cte with check contraints

* replace check contraints with schema lowercase identifiers

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: samrose <samuel.rose@gmail.com>

skills/postgres-best-practices/rules/security-rls-basics.md

@@ -0,0 +1,50 @@
+---
+title: Enable Row Level Security for Multi-Tenant Data
+impact: MEDIUM-HIGH
+impactDescription: Database-enforced tenant isolation, prevent data leaks
+tags: rls, row-level-security, multi-tenant, security
+---
+
+## Enable Row Level Security for Multi-Tenant Data
+
+Row Level Security (RLS) enforces data access at the database level, ensuring users only see their own data.
+
+**Incorrect (application-level filtering only):**
+
+```sql
+-- Relying only on application to filter
+select * from orders where user_id = $current_user_id;
+
+-- Bug or bypass means all data is exposed!
+select * from orders;  -- Returns ALL orders
+```
+
+**Correct (database-enforced RLS):**
+
+```sql
+-- Enable RLS on the table
+alter table orders enable row level security;
+
+-- Create policy for users to see only their orders
+create policy orders_user_policy on orders
+  for all
+  using (user_id = current_setting('app.current_user_id')::bigint);
+
+-- Force RLS even for table owners
+alter table orders force row level security;
+
+-- Set user context and query
+set app.current_user_id = '123';
+select * from orders;  -- Only returns orders for user 123
+```
+
+Policy for authenticated role:
+
+```sql
+create policy orders_user_policy on orders
+  for all
+  to authenticated
+  using (user_id = auth.uid());
+```
+
+Reference: [Row Level Security](https://supabase.com/docs/guides/database/postgres/row-level-security)