TUI for toggling followed artists; musup <N> keeps CLI mode

[Jason-Abbott]

Overview

Change CLI behavior:

• musup <number> — same as today: show all artists and albums new within N years
• musup (no argument) — open a Bubble Tea TUI showing all album artists (using existing is_album_artist filtering) in 3 columns, navigable with arrow keys (up/down/across), with space bar to toggle "follows" checkmark

Tasks

• Add followed boolean column to artists table (new DB migration v14)
• Add Bubble Tea + Lip Gloss + Bubbles dependencies to go.mod
• Create TUI in internal/tui/ package
  • 3-column layout of all album artists
  • Arrow key navigation (up, down, left, right across columns)
  • Space bar toggles followed status (standard checkmark display)
  • Persist follows to DB on toggle
• Update cmd/root.go: if no args → launch TUI; if <number> arg → current CLI behavior
• Add DB queries: list all album artists with followed status, toggle followed
• Tests for new DB queries and migration

Summary of Changes

• Added followed column to artists table (migration v14, default=1)
• Added AlbumArtists and SetFollowed sqlc queries
• Created internal/tui/tui.go with Bubble Tea v2 3-column artist list
• musup (no args) opens TUI; musup <N> keeps CLI behavior
• Added tests for new queries; all tests pass, lint clean

Additional Changes (artist_id FK + modal)

• Migration v15: add artist_id FK to files table, backfill from artist_norm join
• Updated all queries (NewerReleases, AlbumArtists, DistinctArtistIDs) to use artist_id
• Updated scan.go to call EnsureArtist and set artist_id on file upsert
• Updated check.go to use DistinctArtistIDs and pass artist ID directly
• Added ArtistLocalTracks query and GetArtistByID query
• Added enter-key modal showing local albums/tracks for selected artist
• All tests updated and passing, lint clean

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