fix: render markdown links as clickable HTML in Matrix messages

_md_to_html now converts [text](url) to <a> tags and auto-links bare URLs.
Also instructs LLM to use markdown links instead of raw URLs.

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

bot.py

@@ -122,7 +122,8 @@ class DocumentRAG:
             parts.append("")  # blank line between docs
 
         parts.append("Use the document content above to answer the user's question. "
-                      "Always include document links when referencing documents.")
+                      "When referencing documents, use markdown links: [Document Title](url). "
+                      "Never show raw URLs.")
         return "\n".join(parts)
 
 
@@ -581,6 +582,15 @@ class Bot:
         safe = re.sub(r"\*\*(.+?)\*\*", r"<strong>\1</strong>", safe)
         # Italic
         safe = re.sub(r"\*(.+?)\*", r"<em>\1</em>", safe)
+        # Markdown links [text](url) — must unescape the URL parts first
+        def _link_repl(m):
+            import html as _h
+            label = m.group(1)
+            url = _h.unescape(m.group(2))
+            return f'<a href="{url}">{label}</a>'
+        safe = re.sub(r"\[([^\]]+)\]\(([^)]+)\)", _link_repl, safe)
+        # Bare URLs (not already in an <a> tag)
+        safe = re.sub(r'(?<!href=")(?<!">)(https?://[^\s<]+)', r'<a href="\1">\1</a>', safe)
         # Line breaks
         safe = safe.replace("\n", "<br/>")
         return safe