fix: address audit findings — SDK plumbing, TUI bus, dead code

Critical fixes:

- ``StrixOrchestrationHooks.on_agent_start`` now finds the
  ``CaidoCapability`` via ``ctx.context['caido_capability']`` instead
  of ``agent.capabilities`` (we use plain ``Agent``, not
  ``SandboxAgent``, so the latter never existed). The session
  manager's bundle already exposes the capability; ``run_strix_scan``
  threads it through ``make_agent_context`` and ``create_agent``
  forwards it to children.

- ``run_strix_scan`` registers the ``StrixTracingProcessor`` with the
  SDK's tracing provider via ``add_trace_processor`` so SDK trace
  spans hit ``run_dir/events.jsonl`` (was previously a parallel stream
  the SDK ignored).

- ``on_llm_end`` now writes to ``Tracer.record_llm_usage`` in
  addition to ``bus.record_usage`` so the CLI/TUI stats panel sees
  real numbers instead of zeros.

- ``run_strix_scan`` accepts an externally-built ``AgentMessageBus``
  + an explicit ``model`` arg. The TUI pre-creates the bus so its
  stop and chat-input handlers can submit ``bus.send`` /
  ``bus.cancel_descendants`` coroutines onto the scan thread's loop
  via ``asyncio.run_coroutine_threadsafe`` — replacing the
  TODO-stub no-ops.

- ``model`` config now propagates root → context → child agents in
  ``create_agent`` (was hardcoded fallback).

Dead-code removal:

- Deleted the ``load_skill`` tool entirely (host module, sandbox
  module, TUI renderer, tests). The legacy implementation reached
  into a global ``_agent_instances`` registry that no longer exists;
  the post-migration stub returned ``success=True`` without
  injecting anything — pure theater. Skills are still preloaded via
  the system prompt at scan-bring-up.

- Dropped ``tenacity`` and ``xmltodict`` from
  ``[project.dependencies]`` — neither is imported anywhere
  post-migration.

- Stripped the system prompt's "use the load_skill tool" lines.

Tests: 278/278 passing. Removed two ``load_skill`` test cases and a
``test_tool_registration_modes::test_load_skill_import_...`` assertion
that exercised the deleted module.

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

uv.lock

@@ -5441,10 +5441,8 @@ dependencies = [
     { name = "requests" },
     { name = "rich" },
     { name = "scrubadub" },
-    { name = "tenacity" },
     { name = "textual" },
     { name = "traceloop-sdk" },
-    { name = "xmltodict" },
 ]
 
 [package.optional-dependencies]
@@ -5501,11 +5499,9 @@ requires-dist = [
     { name = "requests", specifier = ">=2.32.0" },
     { name = "rich" },
     { name = "scrubadub", specifier = ">=2.0.1" },
-    { name = "tenacity", specifier = ">=9.0.0" },
     { name = "textual", specifier = ">=6.0.0" },
     { name = "traceloop-sdk", specifier = ">=0.53.0" },
     { name = "uvicorn", marker = "extra == 'sandbox'" },
-    { name = "xmltodict", specifier = ">=0.13.0" },
 ]
 provides-extras = ["vertex", "sandbox"]
 
@@ -6081,15 +6077,6 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/3a/0c/3662f4a66880196a590b202f0db82d919dd2f89e99a27fadef91c4a33d41/xlsxwriter-3.2.9-py3-none-any.whl", hash = "sha256:9a5db42bc5dff014806c58a20b9eae7322a134abb6fce3c92c181bfb275ec5b3", size = 175315, upload-time = "2025-09-16T00:16:20.108Z" },
 ]
 
-[[package]]
-name = "xmltodict"
-version = "1.0.4"
-source = { registry = "https://pypi.org/simple" }
-sdist = { url = "https://files.pythonhosted.org/packages/19/70/80f3b7c10d2630aa66414bf23d210386700aa390547278c789afa994fd7e/xmltodict-1.0.4.tar.gz", hash = "sha256:6d94c9f834dd9e44514162799d344d815a3a4faec913717a9ecbfa5be1bb8e61", size = 26124, upload-time = "2026-02-22T02:21:22.074Z" }
-wheels = [
-    { url = "https://files.pythonhosted.org/packages/38/34/98a2f52245f4d47be93b580dae5f9861ef58977d73a79eb47c58f1ad1f3a/xmltodict-1.0.4-py3-none-any.whl", hash = "sha256:a4a00d300b0e1c59fc2bfccb53d7b2e88c32f200df138a0dd2229f842497026a", size = 13580, upload-time = "2026-02-22T02:21:21.039Z" },
-]
-
 [[package]]
 name = "yarl"
 version = "1.23.0"