Add CI workflow, full env docs, fix Up button navigation

- .gitea/workflows/build.yaml: Gitea Actions — push latest on main
- docker-compose.example.yml: image-based pull, all NAT20_ vars shown
- settings.py: add NAT20_PLAYER_RECAP_STYLE / CUSTOM_PROMPT overrides
- README.md: full env var reference table with accepted values + rationale
- files.py: fix parent_path to avoid up-button bug; add path traversal guard
- Files.tsx: remove copy/paste/autoPlay, scope to campaign

backend/app/routers/settings.py

@@ -25,6 +25,8 @@ _ENV_OVERRIDES = {
     "chunk_word_target": "NAT20_CHUNK_WORD_TARGET",
     "world_context": "NAT20_WORLD_CONTEXT",
     "world_context_path": "NAT20_WORLD_CONTEXT_PATH",
+    "player_recap_style": "NAT20_PLAYER_RECAP_STYLE",
+    "player_recap_custom_prompt": "NAT20_PLAYER_RECAP_CUSTOM_PROMPT",
 }
 
 _BOOL_KEYS = {"onboarding_completed"}