Add missing relations to vote_response FGA type

Add project, writer, and viewer relations to vote_response to
match what the voting-service sends via lfx.fga-sync.update_access.
These missing relations caused 2,658 failed batch writes per 24h.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Issue: LFXV2-1554
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Trevor Bramwell <tbramwell@linuxfoundation.org>

Author: bramwelt

charts/lfx-platform/templates/openfga/model.yaml

@@ -307,11 +307,12 @@ spec:
         type vote_response
           relations
             define vote: [vote]
+            define project: [project]
             # owner is the user who cast this response
             define owner: [user]
-            # we don't need to create a "writer" relation that is defined as just "owner":
-            # we just use the "owner" relation in our access checks!
+            define writer: [user] or owner
             define auditor: owner or auditor from vote
+            define viewer: [user:*, user] or auditor
 
         type survey
           relations