feat(voice): all file types + images in voice context (MAT-10)

Generalize PDF-only voice context to support all document types:
- Rename _room_pdf_context → _room_document_context (list-based, 5 cap)
- Handle .docx (python-docx), .txt, .md, .csv, .json, .xml, .html, .yaml, .log
- Store AI image descriptions for voice context
- Multi-document context building with type labels and per-type truncation
- _respond_with_ai now returns reply text for caller use

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

requirements.txt

@@ -9,3 +9,4 @@ canonicaljson>=2.0,<3.0
 httpx>=0.27,<1.0
 openai>=2.0,<3.0
 pymupdf>=1.24,<2.0
+python-docx>=1.0,<2.0