chore: improve agent readiness — AGENTS.md, dependabot, CODEOWNERS, labels

- Add AGENTS.md with build commands, project structure, conventions
- Add .github/dependabot.yml for automated pip + actions updates
- Add .github/CODEOWNERS for review routing
- Expand .gitignore (.env, .DS_Store, IDE configs, coverage, venvs)
- Add C901 complexity rule to ruff (max-complexity=25, benchmarks excluded)
- Add --durations=10 to pytest CI for test performance tracking
- Add docs/schema.sql for knowledge graph schema documentation
- Created P0-P3 priority + area/* + security/performance/docs labels

docs/schema.sql

@@ -0,0 +1,36 @@
+-- MemPalace Knowledge Graph Schema
+-- SQLite database at ~/.mempalace/knowledge_graph.db
+
+CREATE TABLE IF NOT EXISTS entities (
+    id TEXT PRIMARY KEY,
+    name TEXT NOT NULL,
+    type TEXT DEFAULT 'unknown',
+    properties TEXT DEFAULT '{}'
+);
+
+CREATE TABLE IF NOT EXISTS triples (
+    id TEXT PRIMARY KEY,
+    subject TEXT NOT NULL,
+    predicate TEXT NOT NULL,
+    object TEXT NOT NULL,
+    valid_from TEXT,
+    valid_to TEXT,
+    confidence REAL DEFAULT 1.0,
+    source_closet TEXT,
+    source_file TEXT
+);
+
+CREATE TABLE IF NOT EXISTS attributes (
+    entity_id TEXT NOT NULL,
+    key TEXT NOT NULL,
+    value TEXT,
+    valid_from TEXT,
+    valid_to TEXT,
+    PRIMARY KEY (entity_id, key, valid_from)
+);
+
+-- Indexes
+CREATE INDEX IF NOT EXISTS idx_triples_subject ON triples(subject);
+CREATE INDEX IF NOT EXISTS idx_triples_object ON triples(object);
+CREATE INDEX IF NOT EXISTS idx_triples_predicate ON triples(predicate);
+CREATE INDEX IF NOT EXISTS idx_triples_valid ON triples(valid_from, valid_to);