Add tag editing and PDF preview to documents feature

Each document's tags are now editable inline: click Edit to enter a tag
editor (Enter/comma to add, × to remove, Save to persist). The View
button opens the PDF in a new browser tab via blob URL. Both features
work through the existing proxy — no proxy changes needed.

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

features/doc-service/app/schemas/document.py

@@ -37,3 +37,7 @@ class DocumentStatusOut(BaseModel):
 
 class DocumentTypeUpdate(BaseModel):
     document_type: str
+
+
+class TagsUpdate(BaseModel):
+    tags: list[str]