bakery: add stable/beta/dev build tracks

Adds a track concept to bakery (separate from the existing bakery/pacman
distribution channel): stable (unchanged tag-triggered releases), beta
(deliberate beta-v* tag promotion), and dev (published on every push to
dev). Each track gets its own signed index + artifact tree under
dl.breadway.dev so stable's paths and existing installs are untouched.

- bakery: new Track type, a global track preference in installed.json
  (defaults to stable via serde, no migration needed), `bakery track
  show`/`set`, a BAKERY_INDEX_BASE_URL override for testing, and a real
  semver comparison in `update` (was a plain string-equality check before).
  ANSI-colored/aligned CLI output (TTY + NO_COLOR aware).
- gen-index.sh: TRACK env var selects which subtree to read/write.
- CI: dev-bakery.yml/beta-bakery.yml/dev-bread-theme.yml/beta-bread-theme.yml
  publish those two products on the new tracks; dev/beta skip the GitHub
  Release upload step (no per-commit release spam).
- docs/release-channels.md documents the three-track policy.

bakery/Cargo.toml

@@ -19,6 +19,7 @@ hex = { workspace = true }
 clap = { workspace = true }
 chrono = { workspace = true }
 minisign-verify = { workspace = true }
+semver = { workspace = true }
 
 [dev-dependencies]
 tempfile = "3"