feat(logging): per-scan `{run_dir}/strix.log` with scan/agent context tagging

Every scan now writes a complete log file at ``{run_dir}/strix.log``
captured from the moment ``run_dir`` is resolved through teardown.
Stdlib ``logging`` only — no parallel framework.

New ``strix/telemetry/logging.py``:
  * ``setup_scan_logging(run_dir, debug=)`` attaches a ``FileHandler``
    (DEBUG, all ``strix.*``) plus a ``StreamHandler`` (ERROR by
    default; DEBUG via ``STRIX_DEBUG=1``).
  * ``ContextVar``-backed ``scan_id`` and ``agent_id`` injected by a
    ``Filter`` so every line is auto-tagged across asyncio tasks
    without callers passing them explicitly.
  * Third-party noise (``httpx``, ``litellm``, ``openai``,
    ``anthropic``, ``urllib3``, ``httpcore``) capped at WARNING.
  * Returns a teardown handle for ``finally`` cleanup.

Wiring:
  * ``orchestration/scan.py`` calls ``setup_scan_logging`` once per
    scan after ``run_dir`` resolves; sets scan_id; tears down in
    ``finally``. Adds INFO logs for sandbox bring-up + scan
    start/end.
  * ``orchestration/hooks.py`` sets/clears ``agent_id`` ContextVar in
    ``on_agent_start`` / ``on_agent_end`` and emits INFO for agent
    lifecycle, DEBUG for every tool start/end and LLM call.
  * ``interface/main.py`` drops the ``setLevel(ERROR)`` silencer.

Coverage expanded across ~20 files (orchestration, agents, runtime,
llm, tools, interface, config, skills) with INFO for lifecycle and
DEBUG for verbose detail. Per the system instructions in
``logger.warning(f"…{e}")`` were converted to module logger calls.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

strix/config/loader.py

@@ -9,6 +9,7 @@ from __future__ import annotations
 
 import contextlib
 import json
+import logging
 import os
 from pathlib import Path
 from typing import TYPE_CHECKING, Any
@@ -22,6 +23,9 @@ if TYPE_CHECKING:
     from pydantic.fields import FieldInfo
 
 
+logger = logging.getLogger(__name__)
+
+
 _DEFAULT_PATH: Path = Path.home() / ".strix" / "cli-config.json"
 _override: Path | None = None
 _cached: Settings | None = None
@@ -34,8 +38,15 @@ def load_settings() -> Settings:
     """
     global _cached  # noqa: PLW0603
     if _cached is None:
-        init_kwargs: dict[str, Any] = _read_json_overrides(_override or _DEFAULT_PATH)
+        source_path = _override or _DEFAULT_PATH
+        init_kwargs: dict[str, Any] = _read_json_overrides(source_path)
         _cached = Settings(**init_kwargs)
+        logger.debug(
+            "load_settings: resolved (override=%s, file_used=%s, json_keys=%d)",
+            _override is not None,
+            source_path.exists(),
+            sum(len(v) for v in init_kwargs.values()),
+        )
     return _cached
 
 
@@ -44,6 +55,7 @@ def apply_config_override(path: Path) -> None:
     global _override, _cached  # noqa: PLW0603
     _override = path
     _cached = None
+    logger.info("config override applied: %s", path)
 
 
 def persist_current() -> None: