fix: verstak:// links in preview, case-insensitive search, keyboard layout swap

1. Fix verstak:// links rendered as blocked/strikethrough in markdown preview:
   - Changed href from 'javascript:void(0)' to hash-based '#verstak-type-id'
   - DOMPurify no longer strips the link; click handler uses data-verstak-href
   - CSS already handles .md-link--internal with cyan color, no strikethrough

2. Add markdown label escaping for internal link picker:
   - New escapeMarkdownLabel() in markdown.ts escapes [ ] ( )
   - Applied in InternalLinkPicker.selectResult() before inserting markdown

3. Fix case-insensitive search for RU/EN:
   - Add title_lower column (migration 019) populated by Go strings.ToLower
   - BackfillTitleLower() runs after migrations to populate existing rows
   - Search() now queries title_lower with Go-level lowercase (Unicode-aware)
   - insertNode() and UpdateTitle() populate title_lower automatically
   - New migration 019 + BackfillTitleLower in storage.go
   - Tests: TestSearchCaseInsensitive, TestSearchFindsCreatedNode

4. Add keyboard layout swap search support:
   - New keyboardLayout.ts utility with RU↔EN QWERTY mapping
   - expandKeyboardVariants() generates original + swapped + lowercased variants
   - InternalLinkPicker.search() queries all variants in parallel, deduplicates by ID
   - Examples: dthcnfr → верстак, руддщ → hello

Files changed:
- markdown.ts: hash href + escapeMarkdownLabel export
- InternalLinkPicker.svelte: label escaping + layout swap search
- keyboardLayout.ts: new RU/EN layout swap utility
- repository.go: title_lower in Search/insertNode/UpdateTitle
- storage.go: migration019 + BackfillTitleLower
- migrations_019.sql.go: new migration
- search_test.go, repository_test.go: new tests

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

@@ -1,5 +1,7 @@
 <script>
   import { createEventDispatcher } from 'svelte';
+  import { escapeMarkdownLabel } from '../../markdown/markdown';
+  import { expandKeyboardVariants } from '../../util/keyboardLayout';
 
   export let visible = false;
 
@@ -23,14 +25,9 @@
 
   // Map node types from backend to our filter types
   function nodeTypeToFilter(type) {
-    // case, project, client, document, recipe, space → case
-    // note → note
-    // file → file
-    // secret → secret
     if (type === 'note') return 'note';
     if (type === 'file') return 'file';
     if (type === 'secret') return 'secret';
-    // Everything else goes to "case"
     return 'case';
   }
 
@@ -42,9 +39,32 @@
     loading = true;
     error = '';
     try {
-      const res = await window['go']['main']['App']['SearchNodes'](query.trim()) || [];
+      // Expand query with keyboard layout variants for tolerant search
+      const variants = expandKeyboardVariants(query.trim());
+      // Deduplicate: skip variants identical to the original query's lowercase
+      const seen = new Set();
+      const queries = [];
+      for (const v of variants) {
+        if (!seen.has(v)) {
+          seen.add(v);
+          queries.push(v);
+        }
+      }
+      // Execute all variant queries in parallel
+      const allResults = await Promise.all(
+        queries.map(q => window['go']['main']['App']['SearchNodes'](q).catch(() => []))
+      );
+      // Merge and deduplicate by node ID
+      const merged = new Map();
+      for (const arr of allResults) {
+        for (const n of (arr || [])) {
+          if (!merged.has(n.id)) {
+            merged.set(n.id, n);
+          }
+        }
+      }
       // Filter by active type
-      results = res.filter(n => nodeTypeToFilter(n.type) === activeType);
+      results = Array.from(merged.values()).filter(n => nodeTypeToFilter(n.type) === activeType);
       selectedIndex = 0;
     } catch (e) {
       error = String(e);
@@ -77,7 +97,8 @@
   }
 
   function selectResult(item) {
-    const md = `[${item.title}](verstak://${nodeTypeToFilter(item.type)}/${item.id})`;
+    const label = escapeMarkdownLabel(item.title || item.id);
+    const md = `[${label}](verstak://${nodeTypeToFilter(item.type)}/${item.id})`;
     dispatch('insert', { markdown: md });
   }