Update GIF guide with nginx troubleshooting section

Added detailed troubleshooting section for the nginx configuration
issue that caused 404 errors for GIF files.

Changes:
- Added new troubleshooting subsection: 'GIFs return 404 but files exist'
- Documented the nginx regex problem and solution
- Included before/after nginx configuration examples
- Explained negative lookahead regex pattern
- Updated Docker image digest to latest version
- Added latest commit reference (bc688e5)

This helps future admins understand and debug similar nginx routing
issues where static asset caching interferes with backend proxying.

Co-Authored-By: Auggie

GIF_REGENERATION_GUIDE.md

@@ -143,6 +143,29 @@ For each video in the database, the system will:
 - Ensure `/uploads/gifs/` directory is writable
 - Check file ownership and permissions
 
+### GIFs return 404 but files exist on server
+
+This was a nginx configuration issue (fixed in commit bc688e5):
+
+**Problem:** nginx regex for static assets was catching ALL `.gif` files, including those in `/uploads/gifs/`, and trying to serve them from frontend `dist/` directory instead of proxying to backend.
+
+**Solution:** Updated nginx.conf to exclude `/uploads/` path from static asset caching:
+```nginx
+# Before (broken):
+location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
+    expires 1y;
+    add_header Cache-Control "public, immutable";
+}
+
+# After (fixed):
+location ~* ^/(?!uploads/).*\.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
+    expires 1y;
+    add_header Cache-Control "public, immutable";
+}
+```
+
+The negative lookahead `(?!uploads/)` ensures files under `/uploads/` are proxied to backend, not served as static assets.
+
 ## Technical Details
 
 - **GIF Generator:** Uses ffmpeg with two-pass palette optimization
@@ -167,5 +190,6 @@ Use Option 1 (Web UI) or Option 2 (Docker env var) from above.
 
 **Last updated:** 2026-01-18
 **Docker image:** `git.matijaturk.from.hr/johnny2211/znakovni.hr:latest`
-**Digest:** `sha256:5deeaa941152012c5c49823de607b365656ca21cdccb2d914a66e00497d45c9f`
+**Digest:** `sha256:9d17eac2038678e8b65d54eb8a5f1b99974810f829ff414288deb849876db620`
+**Latest commit:** `bc688e5` - Fix nginx configuration for GIF serving