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>

web/build.mjs

@@ -2,6 +2,7 @@
 // file and nothing else), with CSS, JS, fonts and the favicon all inlined.
 import { build, transform } from 'esbuild';
 import { readFile, writeFile, mkdir } from 'node:fs/promises';
+import { createHash } from 'node:crypto';
 import { dirname, join } from 'node:path';
 import { fileURLToPath } from 'node:url';
 
@@ -33,8 +34,29 @@ async function fontFaces(weights) {
   return faces.join('\n');
 }
 
+// The file viewer's editor (devdesk#19): its own IIFE, served over the ttyd
+// channel by `devdesk attach --asset editor.js` and cached by the browser. The
+// page carries its SHA-256, which is both the integrity check and the cache key.
+async function editorBundle() {
+  const out = await build({
+    entryPoints: [at('web', 'editor', 'index.js')],
+    bundle: true,
+    minify: true,
+    format: 'iife',
+    globalName: 'DevDeskEditor',
+    target: ['es2020'],
+    write: false,
+    legalComments: 'eof',
+  });
+  const code = out.outputFiles[0].text;
+  await mkdir(at('dist', 'assets'), { recursive: true });
+  await writeFile(at('dist', 'assets', 'editor.js'), code);
+  return { sha: createHash('sha256').update(code).digest('hex'), size: Buffer.byteLength(code) };
+}
+
 async function main() {
   const ver = await version();
+  const editor = await editorBundle();
 
   const js = await build({
     entryPoints: [at('web', 'src', 'main.js')],
@@ -44,7 +66,10 @@ async function main() {
     target: ['es2020'],
     write: false,
     legalComments: 'eof',
-    define: { __DEVDESK_VERSION__: JSON.stringify(ver) },
+    define: {
+      __DEVDESK_VERSION__: JSON.stringify(ver),
+      __EDITOR_SHA__: JSON.stringify(editor.sha),
+    },
   });
 
   const css = await transform([
@@ -67,6 +92,7 @@ async function main() {
   await mkdir(at('dist'), { recursive: true });
   await writeFile(at('dist', 'index.html'), html);
   console.log(`dist/index.html  ${(html.length / 1024).toFixed(0)} KiB  (devdesk ${ver})`);
+  console.log(`dist/assets/editor.js  ${(editor.size / 1024).toFixed(0)} KiB  sha256 ${editor.sha.slice(0, 12)}`);
 }
 
 main().catch((err) => {