fix(sidebar): sort projects by creation time and auto-scroll while dragging

[130rockirt]

Summary

Fix two sidebar project-list issues:

1. Sort projects by creation date (newest first). The project list previously fell back to alphabetical order (localeCompare on paths). Now the sidebar reads each workspace folder's filesystem creation time (birthtime, with mtime fallback for filesystems without birthtime support) via a new bounded workspace:creation-times IPC channel and sorts project groups newest-first. Projects whose creation time is unavailable sink below dated projects and keep the legacy active-first/name order relative to each other. Explicit user drag ordering (saved in kun.sidebarOrder.v1) still wins when present.

2. Auto-scroll while dragging. HTML5 drag-and-drop never scrolls containers, so when a project list is taller than the sidebar, dragging a row (e.g. dragging zhihu to above kun at the top) could not reach targets outside the viewport. Scroll containers marked data-kun-drag-scroll now auto-scroll when the dragged pointer hovers near their top/bottom edge (capture-phase document listeners, so row-level stopPropagation in drop-position handlers cannot silence it; dragend/drop always stop the scroller).

Changes

• src/main/ipc: new workspace:creation-times handler + workspaceCreationTimesPayloadSchema (max 256 roots, strict, trimmed paths).
• src/shared/kun-gui-api*: WorkspaceCreationTimeEntry type + getWorkspaceCreationTimes surface.
• src/preload: expose getWorkspaceCreationTimes; extract dataMigration into its own module to keep index.ts under the 700-line file gate.
• src/renderer/.../sidebar-project-selectors.ts: compareWorkspacePathsByCreation — newest-first by creation time, undated projects sink, tie/unknown falls back to legacy comparator.
• src/renderer/.../sidebar-project-creation-times.ts: useSidebarWorkspaceCreationTimes hook (identity-keyed, deduped, keeps stale map while refetching to avoid double reshuffle).
• src/renderer/.../sidebar-worktree-discovery.ts: extract useSidebarWorktreeDiscovery hook from SidebarProjectsSection (keeps the file under the 700-line gate after wiring creation times).
• src/renderer/.../sidebar-drag-auto-scroll.ts: edge-proximity velocity + rAF scroller + document-level capture registration; Sidebar.tsx registers it once, projects list container opts in via the attribute.

Tests

• New: sidebar-project-selectors.creation-order.test.ts (ordering, case-insensitive key matching, undated sink, tie active-first, legacy fallback), sidebar-drag-auto-scroll.test.ts (velocity ramp/clamp/minimum, continuous scrolling, stop on middle/drop/dragend, capture-phase), workspace:creation-times handler test (real tmpdir, missing path → null, schema rejection), schema test.
• npm run typecheck ✅
• npm run check:file-lines ✅
• npx eslint on all touched files ✅
• Sidebar selector/drag/order vitest suites (94 tests) ✅; workspace IPC suite ✅
• Full npm run test: all sidebar/preload/IPC/shared tests pass. 20 pre-existing failures in src/main symlink/daemon/migration/installer suites reproduce on a clean origin/develop checkout (Windows sandbox, e.g. daemon-runtime.test.ts fails identically on develop) and are unrelated to this change.