feat: unified, editable frontmatter editor in publish modal

- Preset fields (from settings) are now seeded as editable/deletable rows in
  the modal alongside custom ones, using one consistent row style.
- The note's own merged frontmatter is shown as read-only (disabled) rows at
  the top of the list (only when 'Merge document frontmatter' is on, and only
  for keys not overridden by an editable row).
- Drops the separate read-only 'resolved' text preview; the rows are the
  WYSIWYG result.

Adds pure, unit-tested composeFrontmatter()/docFrontmatterToPairs() and removes
the superseded resolveFrontmatter(). Editable rows are authoritative: on a key
collision they override the merged document field. Presets are deep-copied so
editing rows never mutates saved settings.

Co-Authored-By: Claude

src/frontmatter.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "vitest";
-import { parseNote, resolveFrontmatter, serializeFrontmatter } from "./frontmatter";
+import { composeFrontmatter, docFrontmatterToPairs, parseNote, serializeFrontmatter } from "./frontmatter";
 
 describe("parseNote", () => {
   test("splits frontmatter and body, strips BOM", () => {
@@ -12,27 +12,70 @@ describe("parseNote", () => {
   });
 });
 
-describe("resolveFrontmatter", () => {
-  const presets = [{ key: "layout", value: "post" }, { key: "kind", value: "essay" }];
-  test("presets only when mergeDoc is false", () => {
-    expect(resolveFrontmatter(presets, { title: "X" }, [], false)).toEqual(presets);
-  });
-  test("merge appends doc keys and doc overrides preset value", () => {
-    const r = resolveFrontmatter(presets, { kind: "note", title: "X" }, [], true);
-    expect(r).toEqual([
-      { key: "layout", value: "post" },
-      { key: "kind", value: "note" },
-      { key: "title", value: "X" },
+describe("docFrontmatterToPairs", () => {
+  test("converts a record to ordered string pairs", () => {
+    const pairs = docFrontmatterToPairs({
+      title: "Hello",
+      date: new Date("2026-02-06T00:00:00Z"),
+      draft: true,
+    });
+    expect(pairs).toEqual([
+      { key: "title", value: "Hello" },
+      { key: "date", value: "2026-02-06" },
+      { key: "draft", value: "true" },
     ]);
   });
-  test("custom rows come last and override everything", () => {
-    const r = resolveFrontmatter(presets, {}, [{ key: "layout", value: "page" }], false);
-    expect(r[0]).toEqual({ key: "layout", value: "page" });
-    expect(r).toHaveLength(2);
+  test("empty record yields an empty array", () => {
+    expect(docFrontmatterToPairs({})).toEqual([]);
   });
-  test("date object is rendered as YYYY-MM-DD", () => {
-    const r = resolveFrontmatter([], { date: new Date("2026-06-11T00:00:00Z") }, [], true);
-    expect(r).toEqual([{ key: "date", value: "2026-06-11" }]);
+});
+
+describe("composeFrontmatter", () => {
+  const doc = [
+    { key: "title", value: "Hello" },
+    { key: "date", value: "2026-02-06" },
+  ];
+  const editable = [
+    { key: "layout", value: "post" },
+    { key: "kind", value: "essay" },
+  ];
+
+  test("merge on: document fields first, then editable rows", () => {
+    expect(composeFrontmatter(doc, editable, true)).toEqual([
+      { key: "title", value: "Hello" },
+      { key: "date", value: "2026-02-06" },
+      { key: "layout", value: "post" },
+      { key: "kind", value: "essay" },
+    ]);
+  });
+  test("merge off: only the editable rows", () => {
+    expect(composeFrontmatter(doc, editable, false)).toEqual(editable);
+  });
+  test("an editable row overrides a document field with the same key (doc field dropped)", () => {
+    const ed = [
+      { key: "title", value: "Override" },
+      { key: "layout", value: "post" },
+    ];
+    expect(composeFrontmatter(doc, ed, true)).toEqual([
+      { key: "date", value: "2026-02-06" },
+      { key: "title", value: "Override" },
+      { key: "layout", value: "post" },
+    ]);
+  });
+  test("blank-key editable rows are skipped", () => {
+    const ed = [
+      { key: "", value: "" },
+      { key: "layout", value: "post" },
+      { key: "  ", value: "x" },
+    ];
+    expect(composeFrontmatter([], ed, true)).toEqual([{ key: "layout", value: "post" }]);
+  });
+  test("duplicate editable keys: last value wins at first position", () => {
+    const ed = [
+      { key: "tag", value: "a" },
+      { key: "tag", value: "b" },
+    ];
+    expect(composeFrontmatter([], ed, false)).toEqual([{ key: "tag", value: "b" }]);
   });
 });