Thread stages v0.8.0

Minor Changes

• 28ca086: Prepare Thread stages for an ownership-safe Ribbon sidebar migration. Publish
  the strict stage catalog and migration snapshot/acknowledgement RPCs, freeze a
  versioned compatibility baseline, and persist installation, revision, retained
  order, and ownership metadata. After acknowledgement, keep source placement
  read-only while legacy UI, CLI, shortcuts, automation, undo, and retention use
  Ribbon's authoritative placement or report and reconcile dependency failures.
• 67b3d6b: Fall back to a thread's section icon on its sidebar row. The row still draws its
  project's icon first, but a project nobody has picked an icon for now defers to
  the section the thread is filed under, and falls back to the project's default
  glyph only when neither was picked. A thread takes the nearest section walking up, its own included.

Patch Changes

• 2ff5814: Seed the screenshots from one product in two repositories, filed under a section
  of its own. The shots now picture a section icon, a section crumb, and a sidebar
  focused on one product, none of which the previous fixture could show.

• a25614c: Treat a running background command as active work when switching automatically
  between Idle and Active. The thread returns to Idle only after its last
  background command finishes and no foreground work remains.

• b620fa2: Keep Deferred, Blocked, and Completed threads in their assigned stage when
  their lifecycle status changes. Automatic lifecycle moves now apply only to
  threads already in Idle or Active.

• 67b3d6b: Resolve a thread's section the same way in every plugin: the nearest section
  walking up, the thread's own included. Breadcrumbs took the root's section over
  the thread's own, and Thread stages took the thread's own over any ancestor's,
  so a chain filed at more than one level could show one section's name beside
  another's icon.

• 77f4e11: These plugins now use bb's documented APIs instead of private paths. Calls
  into a neighbouring plugin, a plugin's own settings, and bb's keybinding table
  go through bb.sdk rather than fetched routes.

  Stage chords ask bb to open the composer instead of arranging its stored state
  and faking a keystroke. That needs Thread stages' own list mounted: with bb's
  built-in list selected instead, emptying Idle still files the thread and opens
  a composer, but on the project you last used rather than on none.

• 3606c83: Move everything vendored from BB into each plugin's src/vendor/, so a reader
  can tell BB's code from the plugin's own by its path.

• 3606c83: Refresh every vendored BB component to the pinned registry release, so all
  three plugins share one vintage of BB's menus, overlays, and icons instead of
  two. Breadcrumbs and Icons were carrying components from an older release whose
  pin had been bumped without a re-vendor, which left their overlays a rewrite
  behind and their icon set six icons short.

  The four local edits those copies had accumulated are now composed rather than
  patched in, so no plugin forks BB's UI kit: menus that should stay a dropdown
  on a narrow window use BB's own compact-viewport override, destructive context
  items take the classes BB's app gives them, and the thread filter draws its own
  check and submenu chevron the way its actionable rows already did — which also
  makes its two row types finally render the same selected state.

• 3606c83: Fail the release check when a Tailwind arbitrary variant the source uses never
  reaches the built stylesheet.