docs: add wiki, .env.example, and fix stale if-curator references

- Add docs/setup.md, docs/troubleshooting.md, docs/faq.md as user-facing wiki
- Add .env.example with all env vars and inline comments
- Fix compose.override.yml: rename service if-curator → winnow, update volume paths
- Fix CHANGELOG.md: rename if-curator → winnow in release notes
- Link docs from README

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

compose.override.yml

@@ -1,8 +1,8 @@
 services:
-  if-curator:
+  winnow:
     build: .
     network_mode: host
     volumes:
-      - /code/if-curator/models:/models
-      - /code/if-curator/embeddings:/app/.if_cache
-      - /code/if-curator/output:/app/output
+      - /code/winnow/models:/models
+      - /code/winnow/embeddings:/app/.if_cache
+      - /code/winnow/output:/app/frigate_train