Add project_archives table and MCP tools (CF-264)

- Created migration 009: project_archives table with semantic search
- Implemented archives.ts: archiveAdd, archiveSearch, archiveList, archiveGet
- Registered archive tools in index.ts and tools/index.ts
- Archive types: session, research, audit, investigation, completed, migration
- Uses project_key (TEXT) FK to projects table
- Tested: archive_add and archive_list working correctly

Replaces filesystem archives with database-backed storage.
Eliminates context pollution from Glob/Grep operations.

Task: CF-264
Session: session_20260119111342_66de546b

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

migrations/009_create_project_archives.sql

@@ -0,0 +1,33 @@
+-- Create project_archives table for database-backed archival system
+-- Replaces filesystem archives with searchable, semantic-enabled storage
+
+-- Drop if exists to recreate with correct schema
+DROP TABLE IF EXISTS project_archives;
+
+CREATE TABLE project_archives (
+    id SERIAL PRIMARY KEY,
+    project_key TEXT NOT NULL REFERENCES projects(key),
+    archive_type VARCHAR(50) NOT NULL,
+    title VARCHAR(500) NOT NULL,
+    content TEXT NOT NULL,
+    original_path VARCHAR(1000),
+    file_size INTEGER,
+    archived_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    archived_by_session VARCHAR(100),
+    metadata JSONB DEFAULT '{}',
+    embedding vector(1536),
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
+);
+
+-- Indexes for performance
+CREATE INDEX idx_archives_project ON project_archives(project_key);
+CREATE INDEX idx_archives_type ON project_archives(archive_type);
+CREATE INDEX idx_archives_archived_at ON project_archives(archived_at);
+CREATE INDEX idx_archives_embedding ON project_archives USING ivfflat (embedding vector_cosine_ops);
+CREATE INDEX idx_archives_metadata ON project_archives USING gin(metadata);
+
+-- Archive types: session, research, audit, investigation, completed, migration
+COMMENT ON TABLE project_archives IS 'Database-backed archive storage with semantic search';
+COMMENT ON COLUMN project_archives.archive_type IS 'Type: session, research, audit, investigation, completed, migration';
+COMMENT ON COLUMN project_archives.metadata IS 'JSONB for frontmatter, tags, etc';