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>

web/src/ui.js

@@ -52,7 +52,7 @@ export const dialogOpen = () => openDialogs > 0 || !!document.querySelector('.lt
 // A .lt-modal dialog. `body` is a node; `actions` are { label, value, primary,
 // danger }. Resolves with the chosen action's value (or `submit()`'s value when
 // a form is submitted), or null when dismissed (✕, Esc, backdrop).
-export function openDialog({ title, body, actions = [], danger = false, size = '', onOpen, submit }) {
+export function openDialog({ title, body, actions = [], danger = false, size = '', className = '', onOpen, submit }) {
   return new Promise((resolve) => {
     const opener = document.activeElement;
     let done = false;
@@ -81,7 +81,7 @@ export function openDialog({ title, body, actions = [], danger = false, size = '
       if (button.type === 'submit') button.setAttribute('form', titleId);
     }
     form.id = titleId;
-    const overlay = el('div', { class: 'lt-modal-overlay is-open dd-dialog', role: 'dialog', 'aria-modal': 'true', 'aria-labelledby': `${titleId}-title` },
+    const overlay = el('div', { class: `lt-modal-overlay is-open dd-dialog${className ? ` ${className}` : ''}`, role: 'dialog', 'aria-modal': 'true', 'aria-labelledby': `${titleId}-title` },
       el('div', { class: `lt-modal${size ? ` lt-modal-${size}` : ''}` },
         el('div', { class: `lt-modal-header${danger ? ' lt-modal-header--danger' : ''}` },
           el('h2', { class: 'lt-modal-title', id: `${titleId}-title` }, title),