feat(search): Integrate index cache into search flow

When use_sqlite_cache is disabled, try the binary-index cache first
for literal queries. Regex metacharacters (.+*?|[]{}^$\ etc.) skip
the cache path and go directly to the regex full-scan, preserving
documented regex semantics.

Cache hit: in-memory search (~200ms), no file I/O.
Cache miss: fall back to original regex search (~3s), then build
cache for next invocation.

Also separates the query string from the compiled Regex object,
fixing a latent bug where search_remotes received a Regex instead
of the original string (previously relied on .ToString() coincidence).

Author: B67687

libexec/scoop-search.ps1

@@ -115,6 +115,7 @@ function search_by_index($query) {
             $manifest = Get-Content -Path $info.path -Raw | ConvertFrom-Json -ErrorAction Stop
             $binaries = ''
             $binMatches = @()
+            if (-not $manifest) { continue }
             if ($manifest.bin) {
                 foreach ($binEntry in $manifest.bin) {
                     $exe = $null; $alias = $null
@@ -291,20 +292,34 @@ if (get_config USE_SQLITE_CACHE) {
                 })
         }
 } else {
-    try {
-        $query = New-Object Regex $query, 'IgnoreCase'
-    } catch {
-        abort "Invalid regular expression: $($_.Exception.InnerException.Message)"
+    # Try search index cache first for literal queries (fast, substring matching).
+    # Queries with regex metacharacters skip the cache and go straight to regex.
+    $cacheWasFresh = $false
+    if ($query -notmatch '[.+*?|\[\](){}^$\\]') {
+        $cacheWasFresh = init_search_cache
+        if ($cacheWasFresh) { search_by_index $query }
     }
 
-    $jsonTextAvailable = [System.AppDomain]::CurrentDomain.GetAssemblies() | Where-Object { [System.IO.Path]::GetFileNameWithoutExtension($_.Location) -eq 'System.Text.Json' }
+    # Fall back to regex full-scan when cache produced no results
+    if ($list.Count -eq 0) {
+        try {
+            $regex = New-Object Regex $query, 'IgnoreCase'
+        } catch {
+            abort "Invalid regular expression: $($_.Exception.InnerException.Message)"
+        }
 
-    Get-LocalBucket | ForEach-Object {
-        if ($jsonTextAvailable) {
-            search_bucket $_ $query
-        } else {
-            search_bucket_legacy $_ $query
+        $jsonTextAvailable = [System.AppDomain]::CurrentDomain.GetAssemblies() | Where-Object { [System.IO.Path]::GetFileNameWithoutExtension($_.Location) -eq 'System.Text.Json' }
+
+        Get-LocalBucket | ForEach-Object {
+            if ($jsonTextAvailable) {
+                search_bucket $_ $regex
+            } else {
+                search_bucket_legacy $_ $regex
+            }
         }
+
+        # Build cache for next time only if it wasn't already fresh
+        if (-not $cacheWasFresh) { build_search_cache }
     }
 }