feat: v0.7.0 files pane: browse, preview, diff, Claude's edits

- devdesk attach --fs-list/--fs-read/--git-status/--git-show/--asset
  (libexec/devdesk-files.sh), confined to the session folder.
- The state hook records files Claude edits (Edit/Write/MultiEdit/
  NotebookEdit) for the Changes tab's "C" badge; rename/end carry it.
- Files pane: folders, CodeMirror read-only view, sanitized markdown preview
  in a sandboxed iframe with inlined relative images, images, Changes tab with
  line counts and diff against HEAD, "→ Claude" @path, resizable split.
- The editor bundle ships as /usr/share/devdesk/assets/editor.js, is fetched
  over ttyd on first use, verified against the page's SHA-256 and cached in
  IndexedDB.
- Fix: the state hook's field split collapsed empty fields.

Closes #19

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

libexec/devdesk-lib.sh

@@ -132,7 +132,7 @@ dd_registry_set_claude() {
 
 dd_registry_remove() {
     dd_registry_update 'del(.sessions[$n])' --arg n "$1"
-    rm -f "$DEVDESK_CONTEXT_DIR/$1.json" "$DEVDESK_STATUS_DIR/$1.json"
+    rm -f "$DEVDESK_CONTEXT_DIR/$1.json" "$DEVDESK_STATUS_DIR/$1.json" "$DEVDESK_STATE_DIR/edits/$1.txt"
 }
 
 dd_registry_rename() {
@@ -144,6 +144,9 @@ dd_registry_rename() {
             mv -f "$d/$1.json" "$d/$2.json"
         fi
     done
+    if [ -f "$DEVDESK_STATE_DIR/edits/$1.txt" ]; then
+        mv -f "$DEVDESK_STATE_DIR/edits/$1.txt" "$DEVDESK_STATE_DIR/edits/$2.txt"
+    fi
 }
 
 # Project name (directory or its slug) -> absolute directory inside the projects root.