Fix the possible-duplicates finder; share it as SimilarTicketService (#113)

check_duplicates.php's logic moves to services/SimilarTicketService.php
(used next by the MCP find_similar_tickets tool). Fixes found while
testing it:

- Non-admins never got matches: the query had no `t` alias but the
  visibility filter's SQL uses t.*, so it failed and the error was
  swallowed into "no duplicates".
- The word-overlap scoring could never fire, since candidates were only
  whole-title substring or SOUNDEX matches. Tickets sharing a significant
  word (4+ letters) are now candidates too; overlap needs 2+ shared words
  so one common word (e.g. every automated ticket's [problem] tag) isn't
  a match.
- SOUNDEX compared PHP's 4-char code (effectively the first word) with
  MariaDB's full-length code: the SQL side almost never matched, and the
  scorer marked any two titles sharing a first word as "sounds alike".
  Both sides now use SQL SOUNDEX on the full title.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MGDKHiU5RJdo3dqQUDow3X

api/check_duplicates.php

@@ -8,7 +8,7 @@
 
 require_once __DIR__ . '/bootstrap.php';
 require_once dirname(__DIR__) . '/helpers/ResponseHelper.php';
-require_once dirname(__DIR__) . '/models/TicketModel.php';
+require_once dirname(__DIR__) . '/services/SimilarTicketService.php';
 
 // Only accept GET requests
 if ($_SERVER['REQUEST_METHOD'] !== 'GET') {
@@ -18,100 +18,4 @@ if ($_SERVER['REQUEST_METHOD'] !== 'GET') {
 // Get title parameter
 $title = isset($_GET['title']) ? trim($_GET['title']) : '';
 
-if (strlen($title) < 5) {
-    ResponseHelper::success(['duplicates' => []]);
-}
-
-// Search for similar titles
-// Use both LIKE for substring matching and SOUNDEX for phonetic matching
-$duplicates = [];
-
-// Prepare search term for LIKE
-$searchTerm = '%' . $title . '%';
-
-// Get SOUNDEX of title
-$soundexTitle = soundex($title);
-
-// Build visibility filter so users only see titles they have access to
-$ticketModel = new TicketModel($conn);
-$visFilter = $ticketModel->getVisibilityFilter($currentUser);
-
-// First, search for exact substring matches (case-insensitive)
-$sql = "SELECT ticket_id, title, status, priority, created_at
-        FROM tickets
-        WHERE (
-            title LIKE ?
-            OR SOUNDEX(title) = ?
-        )
-        AND status != 'Closed'
-        AND ({$visFilter['sql']})
-        ORDER BY created_at DESC
-        LIMIT 10";
-
-$types = "ss" . $visFilter['types'];
-$params = array_merge([$searchTerm, $soundexTitle], $visFilter['params']);
-
-// Duplicate detection is advisory (it must not block ticket creation), so on any
-// DB error degrade gracefully to "no duplicates" rather than fataling the request.
-// mysqli may throw (default exception mode) or return false depending on config.
-try {
-    $stmt = $conn->prepare($sql);
-    if (!$stmt) {
-        throw new RuntimeException('prepare failed: ' . $conn->error);
-    }
-    if (!empty($params)) {
-        $stmt->bind_param($types, ...$params);
-    }
-    $stmt->execute();
-    $result = $stmt->get_result();
-    if ($result === false) {
-        // Non-exception mysqli mode: execute/get_result return false instead of
-        // throwing. Treat as a query failure so we don't fatal on $result below.
-        throw new RuntimeException('query failed: ' . $conn->error);
-    }
-} catch (Throwable $e) {
-    error_log('check_duplicates: ' . $e->getMessage());
-    ResponseHelper::success(['duplicates' => []]);
-}
-
-while ($row = $result->fetch_assoc()) {
-    // Calculate similarity score
-    $similarity = 0;
-
-    // Check for exact substring match
-    if (stripos($row['title'], $title) !== false) {
-        $similarity = 90;
-    // Check SOUNDEX match
-    } elseif (soundex($row['title']) === $soundexTitle) {
-        $similarity = 70;
-    // Check word overlap
-    } else {
-        $titleWords = array_map('strtolower', preg_split('/\s+/', $title));
-        $rowWords = array_map('strtolower', preg_split('/\s+/', $row['title']));
-        $matchingWords = array_intersect($titleWords, $rowWords);
-        $similarity = (count($matchingWords) / max(count($titleWords), 1)) * 60;
-    }
-
-    if ($similarity >= 30) {
-        $duplicates[] = [
-            'ticket_id' => $row['ticket_id'],
-            'title' => $row['title'],
-            'status' => $row['status'],
-            'priority' => $row['priority'],
-            'created_at' => $row['created_at'],
-            'similarity' => round($similarity)
-        ];
-    }
-}
-
-$stmt->close();
-
-// Sort by similarity descending
-usort($duplicates, function ($a, $b) {
-    return $b['similarity'] - $a['similarity'];
-});
-
-// Limit to top 5
-$duplicates = array_slice($duplicates, 0, 5);
-
-ResponseHelper::success(['duplicates' => $duplicates]);
+ResponseHelper::success(['duplicates' => SimilarTicketService::find($conn, $currentUser, $title)]);