feat(notes): rich-text editor with tiptap (task 85)

Replace plain textarea with shared tiptap editor and sanitized html rendering.

Adds interactive checklists on read surfaces and mobile overflow fixes.

tests/unit/rich-text.test.ts

@@ -0,0 +1,36 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+import { normalizeNoteBody } from "../../src/components/rich-text/normalize-body";
+import { sanitizeRichTextHtml } from "../../src/components/rich-text/sanitize";
+import { toggleTaskItemInHtml } from "../../src/components/rich-text/toggle-checklist";
+
+describe("normalizeNoteBody", () => {
+  it("wraps plain text paragraphs in HTML", () => {
+    const html = normalizeNoteBody("Hello\n\nWorld");
+    assert.match(html, /<p>Hello<\/p>/);
+    assert.match(html, /<p>World<\/p>/);
+  });
+
+  it("preserves existing HTML", () => {
+    const input = "<p><strong>Bold</strong></p>";
+    assert.equal(normalizeNoteBody(input), input);
+  });
+});
+
+describe("sanitizeRichTextHtml", () => {
+  it("strips script tags", () => {
+    const safe = sanitizeRichTextHtml('<p>Hi</p><script>alert("x")</script>');
+    assert.doesNotMatch(safe, /<script/i);
+    assert.match(safe, /Hi/);
+  });
+});
+
+describe("toggleTaskItemInHtml", () => {
+  it("flips the requested checklist item", () => {
+    const html =
+      '<ul data-type="taskList"><li data-type="taskItem" data-checked="false"><p>One</p></li><li data-type="taskItem" data-checked="false"><p>Two</p></li></ul>';
+    const next = toggleTaskItemInHtml(html, 1, true);
+    assert.match(next, /data-checked="false"/);
+    assert.match(next, /data-checked="true"/);
+  });
+});