e678d1dfdf
Adds the missing UI to change a character tag's fandom, in both places:
- FandomSetDialog (shared): pick an existing fandom, create a new one, or
clear it; on a name collision in the target fandom it surfaces a merge
confirmation and resolves via setFandom(merge:true). Reuses the tags
store's fandom cache.
- TagCard kebab gains "Set fandom…" for character tags (→ TagsView opens
the dialog, reloads on success).
- TagPanel chip kebab gains "Set fandom…" for character tags (→ reloads the
modal's tag list on success).
- tags store: setFandom(tagId, fandomId, {merge}) action + test.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>