feat: full Internal Link Picker with search and type filter

Replace broken ObjectPickerModal and manual modal with proper
InternalLinkPicker component:

- Search field with debounced SearchNodes API calls
- Type tabs: Дело, Заметка, Файл, Секрет (disabled)
- Results list showing title + path, keyboard navigation
- Inserts [Title](verstak://type/id) at cursor position
- No layout breakage — picker is a normal modal via position:fixed
- Escape/Cancel close picker cleanly
- bind:this on NoteEditorPanel → MarkdownEditor.insertText()

Also:
- MarkdownEditor: added public insertText() method + bind:this
- NoteEditorPanel: added bind:this on MarkdownEditor + public insertText()
- Removed manual modal, insertInternalLinkMarkdown(), document.querySelector

frontend/src/lib/components/notes/MarkdownEditor.svelte

@@ -9,6 +9,23 @@
   const dispatch = createEventDispatcher();
   let textareaRef;
 
+  // ─── Public API: insert text at cursor ──────────────────────────
+  export function insertText(text) {
+    const ta = textareaRef;
+    if (!ta) return;
+    const start = ta.selectionStart;
+    const end = ta.selectionEnd;
+    const before = content.substring(0, start);
+    const after = content.substring(end);
+    const newContent = before + text + after;
+    content = newContent;
+    dispatch('content-change', { content: newContent });
+    requestAnimationFrame(() => {
+      ta.focus();
+      ta.selectionStart = ta.selectionEnd = start + text.length;
+    });
+  }
+
   // ─── Core insert helper ──────────────────────────────────────────
   function insertAtCursor(before, after = '', placeholder = '') {
     const ta = textareaRef;