feat: add dedicated TitleField above editor

Adds a TitleField component between the breadcrumb bar and BlockNote
editor that serves as the primary title editing surface. The H1 block
inside BlockNote is hidden via CSS. The title field:
- Shows the note title in a prominent input field
- Displays the expected filename when it differs from the current one
- Triggers onTitleSync on blur/Enter to rename the file
- Responds to laputa:focus-editor selectTitle events for new notes
- Reverts on Escape or empty input

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/Editor.css

@@ -161,3 +161,47 @@
   color: var(--text-faint) !important;
   opacity: 1 !important;
 }
+
+/* --- Title Field --- */
+.title-field {
+  padding: 16px 54px 0;
+  flex-shrink: 0;
+}
+
+.title-field__input {
+  display: block;
+  width: 100%;
+  border: none;
+  outline: none;
+  background: transparent;
+  font-size: var(--editor-title-size, 28px);
+  font-weight: 700;
+  line-height: 1.2;
+  color: var(--foreground);
+  padding: 0;
+}
+
+.title-field__input::placeholder {
+  color: var(--text-faint, #ccc);
+}
+
+.title-field__input:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
+}
+
+.title-field__filename {
+  display: block;
+  font-size: 11px;
+  color: var(--text-faint, #999);
+  margin-top: 2px;
+}
+
+/* Hide the first H1 heading in BlockNote — title is shown in TitleField above */
+.editor__blocknote-container [data-node-type="blockContainer"]:first-child [data-content-type="heading"][data-level="1"] {
+  display: none;
+}
+/* Also hide the BlockContainer wrapper if its heading is hidden */
+.editor__blocknote-container [data-node-type="blockContainer"]:first-child:has([data-content-type="heading"][data-level="1"]) {
+  display: none;
+}