refactor: centralize config & harden security (#141)

* feat: upgrade primary model from llama3.1:8b to qwen2.5:14b

- Swap OLLAMA_MODEL_PRIMARY to qwen2.5:14b for better reasoning
- llama3.1:8b-instruct becomes fallback
- Update .env default and README quick start
- Fix hardcoded model assertions in tests

qwen2.5:14b provides significantly better multi-step reasoning
and tool calling reliability while still running locally on
modest hardware. The 8B model remains as automatic fallback.

* security: centralize config, harden uploads, fix silent exceptions

- Add 9 pydantic Settings fields (skip_embeddings, disable_csrf,
  rqlite_url, brain_source, brain_db_path, csrf_cookie_secure,
  chat_api_max_body_bytes, timmy_test_mode) to centralize env-var access
- Migrate 8 os.environ.get() calls across 5 source files to use
  `from config import settings` per project convention
- Add path traversal defense-in-depth to file upload endpoint
- Add 1MB request body size limit to chat API
- Make CSRF cookie secure flag configurable via settings
- Replace 2 silent `except: pass` blocks with debug logging in session.py
- Remove unused `import os` from brain/memory.py and csrf.py
- Update 5 CSRF test fixtures to patch settings instead of os.environ

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

---------

Co-authored-by: Trip T <trip@local>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/config.py

@@ -106,6 +106,29 @@ class Settings(BaseSettings):
     # In production, security settings are strictly enforced.
     timmy_env: Literal["development", "production"] = "development"
 
+    # ── Test / Diagnostics ─────────────────────────────────────────────
+    # Skip loading heavy embedding models (for tests / low-memory envs).
+    timmy_skip_embeddings: bool = False
+    # Disable CSRF middleware entirely (for tests).
+    timmy_disable_csrf: bool = False
+    # Mark the process as running in test mode.
+    timmy_test_mode: bool = False
+
+    # ── Brain / rqlite ─────────────────────────────────────────────────
+    # URL of the local rqlite node for distributed memory.
+    # Empty string means rqlite is not configured.
+    rqlite_url: str = ""
+    # Source identifier for brain memory entries.
+    brain_source: str = "default"
+    # Path override for the local brain SQLite database.
+    brain_db_path: str = ""
+
+    # ── Security Tuning ───────────────────────────────────────────────
+    # Set to True in production to mark CSRF cookies as Secure (HTTPS only).
+    csrf_cookie_secure: bool = False
+    # Maximum size in bytes for chat API request bodies.
+    chat_api_max_body_bytes: int = 1_048_576  # 1 MB
+
     # ── Self-Modification ──────────────────────────────────────────────
     # Enable self-modification capabilities. When enabled, the agent can
     # edit its own source code, run tests, and commit changes.