fix: media delivery fails for file paths containing spaces (#2621)

Cherry-picked from PR #2583 by Glucksberg.

The MEDIA: regex used \S+ which truncated paths at the first space.
Added a space-aware alternative anchored to known media extensions.
Also updated extract_local_files to allow spaces in path segments.

Follow-up fix: changed \s to [^\S\n] in the space-matching group
so the regex doesn't greedily match across newlines (broke multi-line
MEDIA: tags).

gateway/platforms/base.py

@@ -721,7 +721,7 @@ class BasePlatformAdapter(ABC):
         # Extract MEDIA:<path> tags, allowing optional whitespace after the colon
         # and quoted/backticked paths for LLM-formatted outputs.
         media_pattern = re.compile(
-            r'''[`"']?MEDIA:\s*(?P<path>`[^`\n]+`|"[^"\n]+"|'[^'\n]+'|\S+)[`"']?'''
+            r'''[`"']?MEDIA:\s*(?P<path>`[^`\n]+`|"[^"\n]+"|'[^'\n]+'|(?:~/|/)\S+(?:[^\S\n]+\S+)*?\.(?:png|jpe?g|gif|webp|mp4|mov|avi|mkv|webm|ogg|opus|mp3|wav|m4a)(?=[\s`"',;:)\]}]|$)|\S+)[`"']?'''
         )
         for match in media_pattern.finditer(content):
             path = match.group("path").strip()