feat(manage): add /manage pages to edit caption and date

/manage lists every photo; /manage/edit/{slug} rewrites the photo's
.toml sidecar, which triggers a rebuild. The pages sit behind the same
htpasswd as /upload and are not linked from the public site.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -103,7 +103,7 @@ nix-shell -p apacheHttpd --run \
 | `mlFamily`                  | `Manjari`                          | CSS font-family for the alt-script bio |
 | `nginx.enable`              | `false`                            | Configure an nginx vhost             |
 | `nginx.domain`              | —                                  | Domain for the vhost                 |
-| `nginx.htpasswdFile`        | —                                  | htpasswd file for `/upload`          |
+| `nginx.htpasswdFile`        | —                                  | htpasswd file for `/upload` and `/manage` |
 | `nginx.enableACME`          | `true`                             | Enable Let's Encrypt                 |
 
 ---
@@ -138,3 +138,14 @@ curl -u user:password \
 ```
 
 Or open `https://photos.yourdomain.tld/upload` in a browser.
+
+## Editing a photo
+
+Open `https://photos.yourdomain.tld/manage` in a browser. It lists every
+photo; *Edit* opens a form for the caption and date, and saving rewrites the
+photo's `.toml` sidecar, which triggers a rebuild.
+
+`/manage` sits behind the same htpasswd as `/upload`, and nothing on the
+public site links to it. If you run your own nginx instead of the NixOS
+module, add a `location /manage` block alongside the `/upload` one — without
+it the path is not proxied and returns 404.