fix(ui): prevent search input from clearing on each keystroke and add dedicated /search page

The debounceSearch() function in files.html called clearFullTextSearch()
when the query was shorter than 2 characters. Since clearFullTextSearch()
sets input.value = '', every single keystroke was immediately erased —
users could paste text but not type.

Fix: debounceSearch now only hides the results panel for short queries
without touching the input value.

Also adds a dedicated /search page with Google-style results showing
content previews (document title, filename, type badges, tag badges,
sender, and OCR text snippets with highlighted matches).

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/templates/files.html

@@ -936,7 +936,10 @@
     function debounceSearch(value) {
       clearTimeout(_searchDebounceTimer);
       if (!value || value.trim().length < 2) {
-        clearFullTextSearch();
+        // Only hide the results panel; do NOT clear the input value so the
+        // user can continue typing characters until the query is long enough.
+        var _p = document.getElementById('search-results-panel');
+        if (_p) _p.style.display = 'none';
         return;
       }
       _searchDebounceTimer = setTimeout(() => {