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>

bin/devdesk

@@ -17,6 +17,8 @@ set -euo pipefail
 
 # shellcheck source=libexec/devdesk-lib.sh
 . "${DEVDESK_LIBEXEC:-/usr/lib/devdesk}/devdesk-lib.sh"
+# shellcheck source=libexec/devdesk-files.sh
+. "$DEVDESK_LIBEXEC/devdesk-files.sh"
 
 usage() {
     sed -n '2,12s/^# \{0,1\}//p' "$0"
@@ -316,6 +318,13 @@ cmd_attach() {
         dd_linger
         return
         ;;
+    --fs-list | --fs-read | --git-status | --git-show | --asset)
+        local action=${1#--}
+        shift
+        "cmd_${action//-/_}" "$@"
+        dd_linger
+        return
+        ;;
     --new | --rename | --end)
         local action=${1#--}
         shift