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/llm/multi_provider_setup.py

@@ -10,6 +10,8 @@ through to the SDK's built-in litellm routing.
 
 from __future__ import annotations
 
+import logging
+
 from agents.exceptions import UserError
 from agents.models.interface import Model, ModelProvider
 from agents.models.multi_provider import MultiProvider, MultiProviderMap
@@ -17,6 +19,9 @@ from agents.models.multi_provider import MultiProvider, MultiProviderMap
 from strix.llm.anthropic_cache_wrapper import AnthropicCachingLitellmModel
 
 
+logger = logging.getLogger(__name__)
+
+
 class _AnthropicCachingProvider(ModelProvider):
     """Routes ``anthropic/<model>`` aliases through
     :class:`AnthropicCachingLitellmModel`.
@@ -33,6 +38,7 @@ class _AnthropicCachingProvider(ModelProvider):
                 "Anthropic provider requires a non-empty model name (e.g. 'claude-sonnet-4-6').",
             )
         full = model_name if model_name.startswith("anthropic/") else f"anthropic/{model_name}"
+        logger.debug("Anthropic provider: building cached model for %s", full)
         return AnthropicCachingLitellmModel(model=full)
 
 
@@ -45,4 +51,5 @@ def build_multi_provider() -> MultiProvider:
     """
     pmap = MultiProviderMap()  # type: ignore[no-untyped-call]
     pmap.add_provider("anthropic", _AnthropicCachingProvider())
+    logger.debug("MultiProvider built with anthropic/ caching route")
     return MultiProvider(provider_map=pmap)