Add in-memory result cache with 1-hour TTL

DB is now queried at most once per hour per user; subsequent requests
within the window are served from memory. TTL matches the existing
Cache-Control header. Restart clears the cache immediately.

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

README.md

@@ -64,10 +64,10 @@ Set `OP_TYPES=5,6,7,9,11,18,24` for a more inclusive count.
 - **Template drift.** The harder part. Gitea's `profile.tmpl` does change
   between versions — diff the new upstream against your override on each
   upgrade and re-merge the snippet.
-- **Cache.** 1-hour `Cache-Control` header keeps load trivial. Drop to 5
-  minutes for snappier updates if needed; the underlying query is cheap
-  thanks to the existing index on `(user_id, act_user_id, created_unix)`
-  added in Gitea 1.24.
+- **Cache.** Results are cached in memory for 1 hour (matching the
+  `Cache-Control: max-age=3600` response header), so the DB is only hit
+  once per hour per user regardless of traffic. Restart the service to
+  clear the cache immediately.
 
 ## Local dev