feat(tags): open the tag manager from Settings

Add an "Open tag manager" button under a new Tag library group in Settings →
AI Workspace. It closes Settings and jumps to Explore's tag Manage mode.

To make manage mode reachable from outside the Explore view, lift its flag out
of TagCloud's local state into the store (tagManagerOpen / setTagManagerOpen)
behind an openTagManager() action. Manage mode is reset whenever Explore is
entered normally or the visual-cluster view is selected, so openTagManager()
stays the only path that opens it programmatically.

CHANGELOG.md

@@ -34,7 +34,8 @@ aims to follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html)
 - **Tag management** — Explore → Tag Cloud gains a Manage mode with a flat tag
   list where you can rename a tag, merge it into another (rename it to an
   existing tag's name), or delete it from every image. Changes apply across the
-  whole library.
+  whole library. Settings → AI Workspace also has an "Open tag manager" button
+  that jumps straight into it.
 - **Camera info in the lightbox** — the image info panel now shows EXIF details
   (camera, lens, aperture, shutter, ISO, focal length) and, when a photo is
   geotagged, its GPS coordinates as a link that opens the location in your