perf(tile-cache): fix compression passthrough + 7d TTL + browser caching

- Remove Accept-Encoding stripping — Martin gzip passes through to client
  (was sending uncompressed tiles, wasting bandwidth and cache space)
- Increase cache TTL from 1h to 7d (tiles change only on weekly sync)
- Increase inactive eviction from 24h to 7d
- Add Cache-Control header for browser caching (24h + stale-while-revalidate 7d)
- 204 (empty tiles) cached 1h instead of 1m (they don't change either)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nginx/tile-cache.conf

@@ -5,7 +5,7 @@ proxy_cache_path /var/cache/nginx/tiles
   levels=1:2
   keys_zone=tiles:64m
   max_size=2g
-  inactive=24h
+  inactive=7d
   use_temp_path=off;
 
 server {
@@ -31,16 +31,19 @@ server {
     proxy_set_header Host $host;
     proxy_set_header X-Real-IP $remote_addr;
 
-    # Cache config
+    # Cache config — tiles change only on sync (weekly), long TTL is safe
     proxy_cache tiles;
     proxy_cache_key "$request_uri";
-    proxy_cache_valid 200 1h;
-    proxy_cache_valid 204 1m;
+    proxy_cache_valid 200 7d;
+    proxy_cache_valid 204 1h;
     proxy_cache_valid 404 1m;
     proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
     proxy_cache_lock on;
     proxy_cache_lock_timeout 5s;
 
+    # Browser caching — tiles are immutable between syncs
+    add_header Cache-Control "public, max-age=86400, stale-while-revalidate=604800" always;
+
     # Pass cache status header (useful for debugging)
     add_header X-Cache-Status $upstream_cache_status always;
 
@@ -59,8 +62,7 @@ server {
       return 204;
     }
 
-    # Martin already compresses — pass through
-    proxy_set_header Accept-Encoding "";
+    # Let Martin gzip natively — pass compressed response through to client and cache
     gzip off;
 
     # Timeouts (Martin can be slow on low-zoom tiles)