refactor: delete orphaned dirs, dead streaming infra, unused session/compressor

Orphaned files/dirs:
- ``strix/agents/StrixAgent/`` — empty, only ``__pycache__``.
- ``strix/tools/browser/litellm/`` — empty, only ``__pycache__``.
- ``strix/strix_runs/`` — runtime output left in the working tree.
- ``strix/prompts/`` — single Jinja template that nothing renders.

Dead streaming pipeline (was never wired in the SDK migration):
- Delete ``strix/interface/streaming_parser.py`` (XML tool-call parser
  for an output format the SDK doesn't produce).
- Strip ``streaming_content`` / ``interrupted_content`` dicts and
  five unused methods from ``Tracer``.
- Strip the streaming-render path + ``interrupted`` branch from TUI.
- Trim ``strix/llm/utils.py``: drop ``normalize_tool_format``,
  ``parse_tool_invocations``, ``format_tool_call``,
  ``fix_incomplete_tool_call`` and the XML-stripping in
  ``clean_content``. Keep only the inter-agent-XML scrub.

Unwired session compression:
- Delete ``strix/llm/strix_session.py`` and
  ``strix/llm/memory_compressor.py``. ``Runner.run`` was never called
  with a ``session=``, so the compressor never ran. Drop the matching
  test file and the ``strix_memory_compressor_timeout`` config knob.

Tracer cleanup:
- Remove ``log_agent_creation``, ``log_tool_execution_start``,
  ``update_tool_execution``, ``update_agent_status``,
  ``get_agent_tools`` — none had production callers.
- Rewrite the redaction + correlation tests against
  ``log_chat_message`` (which still emits events).

strix/agents/prompt.py

@@ -1,12 +1,8 @@
 """Jinja-based system-prompt renderer.
 
-Loads ``strix/agents/prompts/system_prompt.jinja`` (508 lines — the
-multi-section production prompt with skills, tools, scan modes, etc.)
-and renders it with the caller's per-run context (scan mode, whitebox,
-interactive, scope authorization block).
-
-References:
-    - HARNESS_WIKI.md §4.1 (system prompt assembly)
+Loads ``strix/agents/prompts/system_prompt.jinja`` and renders it with
+the caller's per-run context (skills, scan mode, whitebox flag,
+interactive flag, scope authorization block).
 """
 
 from __future__ import annotations