M6: lightweight markdown rendering on note cards

Render a small Markdown subset in the read view — headings (#..###), bullet/ordered lists, blockquote, fenced code, and inline **bold** / *italic* / `code` — alongside the existing [[wiki-links]] (task 1905). Capture stays plain text; only the card render is formatted.

Hand-rolled dependency-free parser (notes/markdown.ts) rendered as Vue vnodes (MarkdownText/MarkdownInline), never v-html, so there is no HTML-injection surface — matches the no-heavy-dep ethos. Headings require '# ' (space), so a #tag (no space) stays plain text and is never mistaken for a heading; the two coexist. Replaces LinkedText (links-only) on the card; LinkedText deleted.

Pure frontend — no backend/DB/migration.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

frontend/src/components/NoteCard.vue

@@ -11,7 +11,7 @@ import {
 } from "../notes/colors";
 import type { Note } from "../stores/notes";
 import Icon from "./Icon.vue";
-import LinkedText from "./LinkedText.vue";
+import MarkdownText from "./MarkdownText.vue";
 import NoteChecklist from "./NoteChecklist.vue";
 import { formatReminder, isOverdue } from "../notes/datetime";
 
@@ -175,7 +175,7 @@ onBeforeUnmount(() => document.removeEventListener("mousedown", onDocMousedown))
         {{ note.title }}
       </h3>
       <div v-if="note.body" class="text-sm text-neutral-700 dark:text-neutral-300">
-        <LinkedText :text="note.body" />
+        <MarkdownText :text="note.body" />
       </div>
       <p v-if="!note.title && !note.body && !note.attachments.length" class="text-sm italic text-neutral-400">
         Empty note