chore: add TASK-027 (mouse drag-select in the editor)

@@ -0,0 +1,26 @@
+---
+id: TASK-027
+title: Mouse drag-select in the editor
+status: "\U0001F7E6 Backlog"
+assignee: []
+created_date: '2026-06-29 23:21'
+labels:
+  - feature
+dependencies: []
+priority: medium
+ordinal: 27000
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Implement in-app text selection by mouse: press to anchor, drag (MouseActionMotion) to extend, release to finish — mirroring Shift+arrow selection (respects soft-wrap via MoveToVisual). Currently handleMouse only moves the cursor on left click; there is no drag handling. Also fix the docs/help which already list mouse select as if it works (README Keys table + any in-app help).
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Left press anchors a selection at the click position
+- [ ] #2 Dragging extends the selection to the pointer (soft-wrap aware)
+- [ ] #3 Release leaves the selection active; a plain click with no drag clears it and just moves the cursor
+- [ ] #4 README/help mouse-select claims match actual behavior
+<!-- AC:END -->