feat(gateway): deliverable mode — ship artifacts as native uploads from any agent surface (#27813)

The agent can now produce a chart, PDF, spreadsheet, or any other supported
file type and have it land in Slack / Discord / Telegram / WhatsApp / etc.
as a native attachment, just by mentioning the absolute path in its
response. Same primitive works for kanban-worker completions: workers
attach artifacts via kanban_complete(artifacts=[...]) and the gateway
notifier uploads them alongside the completion message.

Changes:

- gateway/platforms/base.py: extract_local_files now covers PDFs, docx,
  spreadsheets (xlsx/csv/json/yaml), presentations (pptx), archives
  (zip/tar/gz), audio (mp3/wav/...), and html — not just images and video.
  Image/video extensions still embed inline; everything else routes to
  send_document via the existing dispatch partition in gateway/run.py.

- tools/kanban_tools.py + hermes_cli/kanban_db.py: kanban_complete gains
  an explicit ``artifacts`` parameter. The handler stashes it in
  metadata.artifacts (for downstream workers) and the kernel promotes
  it onto the completed-event payload so the notifier can find it
  without a second SQL round-trip.

- gateway/run.py: _kanban_notifier_watcher now calls a new helper
  _deliver_kanban_artifacts after sending the completion text. The
  helper reads payload.artifacts (preferred), falls back to scanning
  the payload summary and task.result with extract_local_files, then
  partitions images / videos / documents and uploads each via
  send_multiple_images / send_video / send_document.

- website/docs/user-guide/features/deliverable-mode.md + sidebars.ts:
  user-facing docs page covering the extension list, the kanban
  artifacts pattern, and the MCP-for-connector-breadth recommendation.

Tests:

- tests/gateway/test_extract_local_files.py: 7 new test cases
  (documents, spreadsheets, presentations, audio, archives, html,
  chart-pdf canonical case). 44 passing, 0 regressions.
- tests/tools/test_kanban_tools.py: 4 new cases covering the artifacts
  arg shape (list / string / merge with existing metadata / type
  rejection). 17 passing.
- tests/hermes_cli/test_kanban_notify.py: 2 new cases covering full
  notifier → artifact-upload path and missing-file silent-skip. 12
  passing.
- E2E (real files, real kanban kernel, real BasePlatformAdapter):
  worker calls kanban_complete(artifacts=[png,pdf,csv]) → metadata +
  event payload land → notifier helper partitions correctly →
  send_multiple_images called once with the PNG, send_document called
  twice with PDF + CSV.

What's NOT in this PR (deferred to follow-ups):

- Ad-hoc "research this for two hours, ping the thread when done"
  slash command — covered today by kanban subscriptions; a dedicated
  slash command can ride a follow-up PR if needed.
- Setup-wizard prompt for recommended MCP servers (Notion, GitHub,
  Linear, etc.) — docs page lists them; UI is a separate change.

Plan and rationale captured in ~/.hermes/docs/perplexity-computer-parity.pdf
(local doc, not shipped).

gateway/platforms/base.py

@@ -2157,12 +2157,20 @@ class BasePlatformAdapter(ABC):
     @staticmethod
     def extract_local_files(content: str) -> Tuple[List[str], str]:
         """
-        Detect bare local file paths in response text for native media delivery.
+        Detect bare local file paths in response text for native delivery.
 
         Matches absolute paths (/...) and tilde paths (~/) ending in common
-        image or video extensions.  Validates each candidate with
-        ``os.path.isfile()`` to avoid false positives from URLs or
-        non-existent paths.
+        image, video, audio, or document extensions.  Validates each
+        candidate with ``os.path.isfile()`` to avoid false positives from
+        URLs or non-existent paths.
+
+        The extension list is broader than just images/video so the agent
+        can produce arbitrary artifacts (charts, PDFs, spreadsheets, code
+        archives, CSVs) and have them ship to the user as native uploads
+        without needing an explicit ``MEDIA:`` tag.  Image / video
+        extensions still embed inline where the platform supports it;
+        document extensions route through ``send_document``.  The dispatch
+        partition lives in ``gateway/run.py``.
 
         Paths inside fenced code blocks (``` ... ```) and inline code
         (`...`) are ignored so that code samples are never mutilated.
@@ -2172,8 +2180,22 @@ class BasePlatformAdapter(ABC):
             raw path strings removed).
         """
         _LOCAL_MEDIA_EXTS = (
-            '.png', '.jpg', '.jpeg', '.gif', '.webp',
+            # Images (embed inline)
+            '.png', '.jpg', '.jpeg', '.gif', '.webp', '.bmp', '.tiff', '.svg',
+            # Video (embed inline where supported)
             '.mp4', '.mov', '.avi', '.mkv', '.webm',
+            # Audio (delivered as voice/audio where supported)
+            '.mp3', '.wav', '.ogg', '.m4a', '.flac',
+            # Documents (uploaded as file attachments)
+            '.pdf', '.docx', '.doc', '.odt', '.rtf', '.txt', '.md',
+            # Spreadsheets / data
+            '.xlsx', '.xls', '.ods', '.csv', '.tsv', '.json', '.xml', '.yaml', '.yml',
+            # Presentations
+            '.pptx', '.ppt', '.odp', '.key',
+            # Archives
+            '.zip', '.tar', '.gz', '.tgz', '.bz2', '.xz', '.7z', '.rar',
+            # Web / rendered output
+            '.html', '.htm',
         )
         ext_part = '|'.join(e.lstrip('.') for e in _LOCAL_MEDIA_EXTS)