feat(notes): move notes with drag and drop, and use the file icon theme

[dionmunk]

Two features from the community fork in #82, rebuilt on top of the current code.

Moving notes and folders

Notes and folders could only be moved outside VS Code (#41).

• Drag and drop: drag notes and folders onto a folder, onto empty space for the top level, or between Workspace Notes and Notes. Select several with Cmd/Ctrl to move them together.
• Move To... in the right-click menu lists every folder of both sections, grouped under "Workspace Notes" and "Notes", leaving out folders an item can't go to.
• Moves go through a WorkspaceEdit, so an open note stays open at its new location.
• A folder can't be moved into itself, an existing item is never overwritten (each case shows a warning), and a note inside a folder that moves too goes along with it.
• Dragging a note onto the editor area opens it (text/uri-list, as the VS Code API recommends).

The drag data is carried as JSON. VS Code only keeps the original objects for drops within the same view, and a drop on the other view delivers our type twice, the first time empty; I confirmed that by logging what handleDrop received, then took the non-empty entry.

File icon theme

Every note showed the same generic file icon. Tree items now carry a resourceUri with the File and Folder theme icons, so VS Code takes the icon from the current file icon theme (by extension for notes, by name for folders).

Testing

• npm test: 26 passing, 4 new tests for the move rules (already there, a folder into itself or a folder inside it, a sibling with a similar name).

• End to end in VS Code 1.140 on macOS, driven with Playwright:

  Scenario	Result
  drag a note onto a folder	moved into the folder
  drag a note from a folder onto empty space	moved to the top level
  drag a note from Notes onto a Workspace Notes folder	moved into .notes/docs
  drag a folder onto a folder inside it	not moved, "can't be moved into itself"
  drag onto a folder that already has that name	not moved, other file untouched, "already exists"
  drag an open note into a folder	tab and breadcrumbs follow it to work/a.md, not shown as deleted
  drag two selected notes	both moved
  Move To...	grouped list of folders in both sections, note moved to work/old
  drag a note onto the editor	note opens
  icons, master / this branch	generic file icon for every note / md, json, py, txt and folder icons from the theme

• The Workspace Notes, Extension does not accept the notes location #69/notes panel keeps asking for 'select location' no mather what i add in the settings #71 and external change scenarios from fix(notes): stop asking for a storage location once one is set #86, feat(notes): keep the Notes view in sync with changes made outside the window #91 and feat(notes): add a Workspace Notes section for per-project notes #93 were re-run with the same results, including New Note and New Folder with a note selected now that the views allow selecting several items.

• Not tested: Windows, Linux, and dragging into the editor with a real mouse rather than Playwright's (a quick synthetic drag doesn't trigger VS Code's editor drop target; a slower one that hovers first does).

Closes #41.