feat: add comprehensive tagging system with cooccurrence tracking

- Add tags, project_tags, and tag_cooccurrence tables with proper indexes
- Implement full CRUD API endpoints for tag management
- Add tag association endpoints for projects with automatic cooccurrence updates
- Include related tags and project filtering by tag functionality

migrations/20260106000000_initial_schema.sql

@@ -0,0 +1,35 @@
+-- Project status enum
+CREATE TYPE project_status AS ENUM ('active', 'maintained', 'archived', 'hidden');
+
+-- Projects table
+CREATE TABLE projects (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    slug TEXT NOT NULL UNIQUE,
+    title TEXT NOT NULL,
+    description TEXT NOT NULL,
+    status project_status NOT NULL DEFAULT 'active',
+    github_repo TEXT,
+    demo_url TEXT,
+    priority INTEGER NOT NULL DEFAULT 0,
+    icon TEXT,
+    last_github_activity TIMESTAMPTZ,
+    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+-- Indexes for common queries
+CREATE INDEX idx_projects_status ON projects(status);
+CREATE INDEX idx_projects_priority ON projects(priority DESC);
+CREATE INDEX idx_projects_slug ON projects(slug);
+
+-- Trigger to auto-update updated_at
+CREATE OR REPLACE FUNCTION update_updated_at_column()
+RETURNS TRIGGER AS $$
+BEGIN
+    NEW.updated_at = NOW();
+    RETURN NEW;
+END;
+$$ language 'plpgsql';
+
+CREATE TRIGGER update_projects_updated_at BEFORE UPDATE ON projects
+    FOR EACH ROW EXECUTE FUNCTION update_updated_at_column();