feat(search): Add in-memory index search function

Add search_by_index() which performs zero-I/O substring matching:
- Iterates cached app names for name matches
- Iterates cached binary names for binary-only matches
- Only JSON-parses manifests for apps that matched
- Guard clause returns early on null/empty query

Uses IndexOf() with OrdinalIgnoreCase for case-insensitive
substring matching, consistent with SQLite LIKE '%query%' behavior.

Author: B67687

libexec/scoop-search.ps1

@@ -91,6 +91,50 @@ function build_search_cache {
     return $true
 }
 
+function search_by_index($query) {
+    if (-not $query) { return }
+    $matched = @{}
+    # Search app names (case-insensitive substring)
+    foreach ($appName in $searchIndexApps.Keys) {
+        if ($appName.IndexOf($query, [StringComparison]::OrdinalIgnoreCase) -ge 0) {
+            if (-not $matched.ContainsKey($appName)) { $matched[$appName] = $true }
+        }
+    }
+    # Search binary names (case-insensitive substring)
+    foreach ($binName in $searchIndexBins.Keys) {
+        if ($binName.IndexOf($query, [StringComparison]::OrdinalIgnoreCase) -ge 0) {
+            foreach ($appName in $searchIndexBins[$binName]) {
+                if (-not $matched.ContainsKey($appName)) { $matched[$appName] = $true }
+            }
+        }
+    }
+    # Parse manifests only for matched apps
+    foreach ($appName in $matched.Keys) {
+        $info = $searchIndexApps[$appName]
+        try {
+            $manifest = Get-Content -Path $info.path -Raw | ConvertFrom-Json -ErrorAction Stop
+            $binaries = ''
+            $binMatches = @()
+            if ($manifest.bin) {
+                foreach ($binEntry in $manifest.bin) {
+                    $exe = $null; $alias = $null
+                    if ($binEntry -is [System.Object[]]) {
+                        $exe = $binEntry[0]
+                        $alias = if ($binEntry.Count -gt 1) { $binEntry[1] } else { $null }
+                    } else { $exe = $binEntry }
+                    $exeName = [System.IO.Path]::GetFileNameWithoutExtension([string]$exe)
+                    if ($exeName.IndexOf($query, [StringComparison]::OrdinalIgnoreCase) -ge 0 -or
+                        ($alias -and $alias.IndexOf($query, [StringComparison]::OrdinalIgnoreCase) -ge 0)) {
+                        $binMatches += [System.IO.Path]::GetFileName([string]$exe)
+                    }
+                }
+                if ($binMatches) { $binaries = $binMatches -join ' | ' }
+            }
+            $list.Add([PSCustomObject]@{ Name = $appName; Version = $manifest.version; Source = $info.bucket; Binaries = $binaries })
+        } catch { }
+    }
+}
+
 function bin_match($manifest, $query) {
     if (!$manifest.bin) { return $false }
     $bins = foreach ($bin in $manifest.bin) {