## Implementation Plan: Paste-to-Upload in Comment Textbox

### Change Required

**File:** `static/js/components/AppUpload.js`

1. In the `connectedCallback()` method, locate the nearest `<textarea>` element within the same parent form. Use `this.closest('form')?.querySelector('textarea[data-mention]')` (the comment textarea is decorated with `data-mention` in the templates). If found, attach a `paste` event listener.

2. In the listener, inspect `event.clipboardData.files`. If it contains any files (`files.length > 0`), call `this.handleFiles(event.clipboardData.files)` without preventing the default paste action (text-only content should still paste normally).

3. Guard against duplicate listener attachment (e.g., set a flag `this._pasteBound = true` after attaching; clear it in `disconnectedCallback()` if needed).

**No other files require modification.** The `<dp-upload>` component already exists in both top-level and reply comment forms (`_comment_form.html`), and the server endpoint `POST /uploads/upload` already accepts multipart uploads from this component.

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### Definition of Done

- [ ] A `paste` event listener is attached to the comment textarea inside the `dp-upload` component, and it forwards clipboard file data to `handleFiles()`.
- [ ] Pasting an image (or any file) from the clipboard into the comment textbox triggers an upload; the attachment appears in the form and can be submitted.
- [ ] Normal text-only pasting continues to work unchanged (no interference).
- [ ] The project’s unit test suite passes:  
      `pip install -e '.[dev]' -q && make test-unit`  
      exits with code 0.
- [ ] The linter passes:  
      `pip install -q ruff && ruff check .`  
      returns zero errors or warnings.
- [ ] Only `static/js/components/AppUpload.js` is modified; no changes to templates, server code, or other JavaScript files.