feat(comments): inline edit on click + trash icon for own comments

Own comments:
- Click the text to open inline edit (textarea replaces text)
- Enter saves, Escape cancels
- Small trash icon always visible in bottom-right corner
- Hover on text shows cursor-text + subtle bg highlight

Other people's comments: read-only, no edit/delete affordances.

Re-add currentUserId prop chain for ownership check.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/documents/[id]/+page.svelte

@@ -9,6 +9,7 @@ let { data } = $props();
 
 const doc = $derived(data.document);
 const canWrite = $derived(data.canWrite ?? false);
+const currentUserId = $derived((data.user?.id as string | undefined) ?? null);
 
 // ── File loading ──────────────────────────────────────────────────────────────
 
@@ -217,6 +218,7 @@ onMount(() => {
 					documentId={doc.id}
 					blocks={transcriptionBlocks}
 					canComment={canWrite}
+					currentUserId={currentUserId}
 					onBlockFocus={handleBlockFocus}
 					onSaveBlock={saveBlock}
 					onDeleteBlock={deleteBlock}