feat: v0.8.0 edit and save files with conflict detection

- devdesk attach --fs-write SESSION PATH BYTES BASESHA|new: streamed like
  uploads, temp file in the same folder, sha re-check (conflict reply instead
  of overwriting), mode/owner kept, atomic mv; new files with folders, never
  outside the session folder or through a symlink out of it.
- Editor: editable CodeMirror for UTF-8 text, dirty tracking, Ctrl+S,
  Save/Revert, conflict dialog with a disk-vs-yours diff, changed-on-disk
  banner, drafts in localStorage (flushed on pagehide), close/leave guards,
  New file.
- Upload streaming factored into streamIn(), shared by uploads and saves.

Closes #20

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

debian/changelog

@@ -1,3 +1,28 @@
+devdesk (0.8.0) bookworm; urgency=medium
+
+  * Edit and save files in the Files pane (#20):
+    - Text files open editable; ● marks unsaved tabs; Ctrl+S or Save writes
+      through `devdesk attach --fs-write`: a temp file in the same folder,
+      mode and owner kept, swapped in with mv.
+    - Conflict detection: the save carries the sha256 of the version you
+      opened; if Claude (or anyone) changed the file since, nothing is written
+      and you choose Compare (diff of disk vs yours), Overwrite or Cancel.
+    - A file that changes on disk while you edit it shows a banner (Compare,
+      Reload, Keep mine) instead of replacing your text; clean files still
+      reload in place.
+    - Unsaved edits are mirrored to the browser as drafts (flushed when the
+      page closes), so a reload, a crash or a session switch doesn't lose
+      them; a draft for a file that changed since offers Compare/Restore/
+      Discard.
+    - Closing a tab with unsaved changes asks Save / Don't save / Cancel;
+      leaving the page warns.
+    - ＋ New file (missing folders are created; never outside the session
+      folder, and never through a symlink out of it).
+    - Markdown previews show unsaved Source edits. Latin-1 files stay
+      read-only.
+
+ -- Jared Vititoe <jjvititoe1@gmail.com>  Sat, 10 Oct 2026 20:09:49 -0400
+
 devdesk (0.7.3) bookworm; urgency=medium
 
   * Fix (#38): links that mean "go to that session" no longer re-create one