feat: reindex button with progress ring in the semantic map titlebar

[lstein]

Summary

• Adds a small refresh button (two circling arrows in pale grey, styled like the neighbouring titlebar icons) immediately left of the album pulldown in the semantic-map window. Clicking it starts an index update for the current album — a shortcut for opening Album Management.
• While the update runs, the button is swapped for a progress ring that fills with the real completion percentage and takes the Album Manager's phase colours (orange scanning/indexing, purple model download, blue UMAP). The directory-traversal phase has no meaningful percentage, so it renders as a spinning indeterminate arc instead.
• Hovering the ring shows the live status text (e.g. "Checking new image files (1,200 of 5,000)... (24%)") via a tooltip refreshed on each poll tick.
• Opening the map window or switching albums attaches the ring to an already-running update (started from Album Management, Update All, or another tab) rather than starting a duplicate. Clicking during a run does nothing — cancellation deliberately stays in Album Management, which has a proper cancel button.
• On completion an albumIndexUpdated event fires and the map reloads itself with the fresh data. On error the plain button returns with the error message in its tooltip and can be clicked to retry.

All new logic lives in a dedicated umap-reindex.js module wired into umap.js; no backend changes.

Test plan

• 7 new Jest tests: button/ring swap and completion event, attach-to-running, failed-start recovery, error-status tooltip, ring colour/fill/title rendering, indeterminate scanning arc, and the ongoing-run check on window open.
• Full frontend suite (394 tests), ESLint, Prettier clean.
• Manually verified against a live album by the author, including the icon styling on the dark titlebar.

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