refactor(db): extract shared DB module from duplicated patterns

Create tooling/db/common.py with resolve_db_path(), load_config(),
get_connection(), and ensure_venv(). Update ticket, sprint,
sqlite_connector.py, and decisions_sync.py to import from common
instead of duplicating. Fixes pre-existing NameError in
decisions_sync.py (missing import os). Add pyproject.toml with
ruff config (ruff==0.15.9, CVE-clean) and dev dependencies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tooling/db/ticket

@@ -23,31 +23,12 @@ All output is JSON on stdout.
 """
 
 import json
-import os
-import sqlite3
 import sys
 from pathlib import Path
 
-SCRIPT_DIR = Path(__file__).resolve().parent
-CONFIG_PATH = SCRIPT_DIR / "config.json"
-WORKTREE_ROOT = (SCRIPT_DIR / ".." / "..").resolve()
-# Database path: SR_DB_PATH env var (absolute), or fallback to parent directory heuristic.
-DB_PATH = Path(os.environ["SR_DB_PATH"]).resolve() if os.environ.get("SR_DB_PATH") else (WORKTREE_ROOT / ".." / "settledreach.db").resolve()
+sys.path.insert(0, str(Path(__file__).resolve().parent))
 
-
-def load_config():
-    with open(CONFIG_PATH, "r") as f:
-        cfg = json.load(f)
-    cfg["sqlite_db_resolved"] = str(DB_PATH)
-    return cfg
-
-
-def get_connection(cfg):
-    conn = sqlite3.connect(cfg["sqlite_db_resolved"])
-    conn.execute("PRAGMA journal_mode=WAL;")
-    conn.execute("PRAGMA foreign_keys=ON;")
-    conn.row_factory = sqlite3.Row
-    return conn
+from common import get_connection, load_config  # noqa: E402
 
 
 def query(conn, sql, params=()):