chore: add skills library

claude-skills/design-postgres-tables.md

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+---
+name: design-postgres-tables
+description: Design PostgreSQL table schemas. Use when modeling new data, adding tables, or reviewing/improving existing schema design.
+---
+
+# Design Postgres Tables Skill
+
+Use when: designing new tables, modeling relationships, reviewing schema, or planning migrations.
+
+## Column Conventions
+- **Primary key**: `id UUID PRIMARY KEY DEFAULT gen_random_uuid()` (prefer UUID over serial for distributed systems; use BIGSERIAL if you need sortable IDs)
+- **Timestamps**: always include `created_at TIMESTAMPTZ DEFAULT NOW()` and `updated_at TIMESTAMPTZ DEFAULT NOW()`
+- **Soft delete**: `deleted_at TIMESTAMPTZ DEFAULT NULL` (NULL = active)
+- **Foreign keys**: name as `<table_singular>_id`, e.g. `user_id`, `project_id`
+- Use `TEXT` over `VARCHAR(n)` unless you need DB-enforced length limits
+- Use `BOOLEAN` not `SMALLINT` for true/false
+- Use `NUMERIC(precision, scale)` for money, never `FLOAT`
+
+## Naming Conventions
+- Tables: `snake_case`, plural: `users`, `project_sessions`, `api_tokens`
+- Columns: `snake_case`, singular
+- Indexes: `idx_<table>_<column(s)>`: `idx_users_email`
+- Foreign keys: `fk_<table>_<referenced_table>`: `fk_orders_users`
+- Unique constraints: `uq_<table>_<column(s)>`: `uq_users_email`
+
+## Standard Table Template
+```sql
+CREATE TABLE items (
+    id          UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    
+    -- Business columns
+    name        TEXT NOT NULL,
+    description TEXT,
+    status      TEXT NOT NULL DEFAULT 'active'
+                CHECK (status IN ('active', 'inactive', 'archived')),
+    
+    -- Relationships
+    user_id     UUID NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    
+    -- Metadata
+    metadata    JSONB DEFAULT '{}',
+    
+    -- Audit
+    created_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at  TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    deleted_at  TIMESTAMPTZ
+);
+
+-- Indexes
+CREATE INDEX idx_items_user_id ON items(user_id);
+CREATE INDEX idx_items_status ON items(status) WHERE deleted_at IS NULL;
+CREATE INDEX idx_items_created_at ON items(created_at DESC);
+
+-- Auto-update updated_at
+CREATE TRIGGER items_updated_at
+    BEFORE UPDATE ON items
+    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();
+```
+
+## Relationship Patterns
+- **One-to-many**: FK on the "many" side
+- **Many-to-many**: junction table with `<a>_id` + `<b>_id` + its own PK + timestamps
+- **Polymorphic**: `entity_type TEXT + entity_id UUID` (add check constraint for valid types)
+
+## Index Strategy
+- Index all foreign keys
+- Index columns used in WHERE clauses with high selectivity
+- Partial indexes for filtered queries: `WHERE deleted_at IS NULL`
+- Composite indexes: put equality columns first, range columns last
+- JSONB: use GIN index for `@>` containment queries
+
+## Design Checklist
+- [ ] Every table has UUID PK + created_at + updated_at
+- [ ] Foreign keys have explicit ON DELETE behavior (CASCADE vs RESTRICT vs SET NULL)
+- [ ] Enum-like columns use CHECK constraints or a lookup table
+- [ ] Money stored as NUMERIC not FLOAT
+- [ ] Indexes on all FK columns
+- [ ] No storing arrays as comma-separated strings (use ARRAY[] or junction table)
+- [ ] JSONB for truly dynamic/schemaless data only — not as a crutch