fix: keyboard layout map, picker type tabs as filters, add unit tests

1. Fix RU_TO_EN keyboard map in keyboardLayout.ts:
   - ч was mapped to 'c' (wrong), now correctly 'x'
   - с was mapped to 'v' (wrong), now correctly 'c'
   - ю was mapped to '.' (wrong), now correctly ','
   - Full rewrite with standard QWERTY/ЙЦУКЕН positional mapping
   - Examples: dthcnfr→верстак, руддщ→hello, цщкдв→world all correct now

2. Root cause of search breaking after 3-4 chars:
   Old map had ч:'c', с:'v' swapped. So dthcnfr → 'верчиак' (wrong).
   Each character was mapped to wrong Cyrillic equivalent.

3. Add unit tests: keyboardLayout.test.js (39 tests, node-runner):
   - EN→RU: dthcnfr, ghbdtn, ntcn
   - RU→EN: руддщ, цщкдв, ышеш
   - Unicode safety: Latin c (U+0063) ≠ Cyrillic с (U+0441)
   - expandKeyboardVariants for mixed inputs
   - Edge cases: empty, single char, mixed case, numbers

4. InternalLinkPicker type tabs → filters (not search modes):
   - Store rawResults (all) + filtered results by activeType
   - Switching type tab no longer clears query or triggers new search
   - Just filters existing rawResults by selected type
   - Shows 'Нет результатов для этого типа' when filtered empty

5. Both GlobalSearch and InternalLinkPicker use same expandKeyboardVariants()

All tests PASS, full build OK.

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

@@ -17,7 +17,8 @@
 
   let activeType = 'note';
   let query = '';
-  let results = [];
+  let rawResults = [];       // all search results (unfiltered)
+  let results = [];          // filtered by activeType
   let selectedIndex = 0;
   let loading = false;
   let error = '';
@@ -31,8 +32,15 @@
     return 'case';
   }
 
+  // Filter rawResults by activeType into displayed results
+  function applyTypeFilter() {
+    results = rawResults.filter(n => nodeTypeToFilter(n.type) === activeType);
+    selectedIndex = 0;
+  }
+
   async function search() {
     if (!query.trim() || query.trim().length < 2) {
+      rawResults = [];
       results = [];
       return;
     }
@@ -41,7 +49,6 @@
     try {
       // 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) {
@@ -63,11 +70,11 @@
           }
         }
       }
-      // Filter by active type
-      results = Array.from(merged.values()).filter(n => nodeTypeToFilter(n.type) === activeType);
-      selectedIndex = 0;
+      rawResults = Array.from(merged.values());
+      applyTypeFilter();
     } catch (e) {
       error = String(e);
+      rawResults = [];
       results = [];
     } finally {
       loading = false;
@@ -104,9 +111,7 @@
 
   function handleTypeChange(typeId) {
     activeType = typeId;
-    query = '';
-    results = [];
-    error = '';
+    applyTypeFilter();
     if (inputRef) inputRef.focus();
   }
 
@@ -159,8 +164,10 @@
           <div class="picker-loading">Загрузка...</div>
         {:else if error}
           <div class="picker-error">{error}</div>
-        {:else if query.trim().length >= 2 && results.length === 0}
-          <div class="picker-empty">Ничего не найдено</div>
+        {:else if query.trim().length >= 2 && results.length === 0 && !loading}
+          <div class="picker-empty">
+            {rawResults.length > 0 ? 'Нет результатов для этого типа' : 'Ничего не найдено'}
+          </div>
         {:else}
           {#each results as item, i}
             <button