Added velocity to tracks in the sequencer.

docs/ROADMAP.md

@@ -3575,6 +3575,43 @@ qualification.
 
 ---
 
+## Phase 109 — Expandable Track Velocity Lanes
+
+### Goal
+
+Expand arrangement tracks downward with a small disclosure arrow and edit MIDI
+note velocities directly below their clips. This user-requested GUI increment
+uses the existing C note-editing, persistence and history contracts.
+
+### Tasks and acceptance criteria
+
+- [x] Add a small arrow beside each track name; independently expand/collapse
+      tracks downward and reposition following clips and instrument selectors.
+- [x] Draw velocity bars for visible note starts in each track's MIDI clips,
+      respecting clip offsets, timeline zoom and scrolling.
+- [x] Drag a bar's cap vertically to preview and commit velocity (1–127), preserving
+      note timing, pitch and channel; Escape cancels and undo/redo restores edits.
+- [x] Preserve expansion by track ID through reordering and ordinary edits;
+      reset it on project replacement. Expansion is temporary GUI state.
+- [x] Verify real FLTK arrow gestures, lane edits, coincident notes, cancellation,
+      undo/redo, shifted clip selection and track reordering in GUI integration tests.
+- [x] Update README guidance and capture actual expanded and compact sequencer
+      screenshots; regenerate the promotional overview.
+
+### Implementation status
+
+Implemented on 2026-11-06 in the FLTK sequencer using the existing C API; no
+engine or project-format changes. Audio-only tracks and buses can expand but
+have no MIDI note bars. Notes beginning before a trimmed clip's visible source
+range are omitted. Coincident notes with different velocities can be selected
+by their caps; fully overlapping caps select one note, with individual editing
+still available in the piano roll. Track expansion is not saved in projects.
+
+Validation: warning-enabled CMake build, CTest GUI integration and offline
+checks, plus rendered screenshot inspection. See [the gallery](../screenshots/README.md).
+
+---
+
 ## Recommended Execution Order
 
 Reorder the phases when the audit reveals a blocking dependency. Do not mark a