feat(read_file): add DOCX, XLSX, PPTX support via document.extract_text()

Wire up the existing office document extractors in document.py to
ReadFileTool by adding an extension guard and _read_office_doc() method
that follows the established PDF pattern. Handles missing libraries,
corrupt files, empty documents, and 128K truncation consistently.

nanobot/agent/tools/filesystem.py

@@ -137,10 +137,11 @@ class ReadFileTool(_FsTool):
     @property
     def description(self) -> str:
         return (
-            "Read a file (text or image). Text output format: LINE_NUM|CONTENT. "
+            "Read a file (text, image, or document). "
+            "Text output format: LINE_NUM|CONTENT. "
             "Images return visual content for analysis. "
-            "Use offset and limit for large files. "
-            "Cannot read non-image binary files. "
+            "Supports PDF, DOCX, XLSX, PPTX documents. "
+            "Use offset and limit for large text files. "
             "Reads exceeding ~128K chars are truncated."
         )
 
@@ -169,6 +170,10 @@ class ReadFileTool(_FsTool):
             if fp.suffix.lower() == ".pdf":
                 return self._read_pdf(fp, pages)
 
+            # Office document support
+            if fp.suffix.lower() in {".docx", ".xlsx", ".pptx"}:
+                return self._read_office_doc(fp)
+
             raw = fp.read_bytes()
             if not raw:
                 return f"(Empty file: {path})"
@@ -304,6 +309,25 @@ class ReadFileTool(_FsTool):
             result = result[:self._MAX_CHARS] + "\n\n(PDF text truncated at ~128K chars)"
         return result
 
+    def _read_office_doc(self, fp: Path) -> str:
+        from nanobot.utils.document import extract_text
+
+        result = extract_text(fp)
+
+        if result is None:
+            return f"Error: Unsupported file format: {fp.suffix}"
+
+        if result.startswith("[error:"):
+            return f"Error reading {fp.suffix.upper()} file: {result}"
+
+        if not result:
+            return f"({fp.suffix.upper().lstrip('.')} has no extractable text: {fp})"
+
+        if len(result) > self._MAX_CHARS:
+            result = result[:self._MAX_CHARS] + "\n\n(Document text truncated at ~128K chars)"
+
+        return result
+
 
 # ---------------------------------------------------------------------------
 # write_file