security: add input sanitization for search queries

- Escape SQL LIKE wildcards (% and _) to prevent pattern injection
- Limit search query length to 100 characters
- Apply sanitization in both :search action and linking filters
- FTS and fuzzy search use unsanitized query (wildcards not special there)

lib/membership/member.ex

@@ -156,12 +156,15 @@ defmodule Mv.Membership.Member do
 
         if is_binary(q) and String.trim(q) != "" do
           q2 = String.trim(q)
-          pat = "%" <> q2 <> "%"
+          # Sanitize for LIKE patterns (escape % and _), limit length to 100 chars
+          q2_sanitized = sanitize_search_query(q2)
+          pat = "%" <> q2_sanitized <> "%"
 
           # Build search filters grouped by search type for maintainability
           # Priority: FTS > Substring > Custom Fields > Fuzzy Matching
+          # Note: FTS and fuzzy use q2 (unsanitized), LIKE-based filters use pat (sanitized)
           fts_match = build_fts_filter(q2)
-          substring_match = build_substring_filter(q2, pat)
+          substring_match = build_substring_filter(q2_sanitized, pat)
           custom_field_match = build_custom_field_filter(pat)
           fuzzy_match = build_fuzzy_filter(q2, threshold)
 
@@ -505,6 +508,31 @@ defmodule Mv.Membership.Member do
     end
   end
 
+  # ============================================================================
+  # Search Input Sanitization
+  # ============================================================================
+
+  # Sanitizes search input to prevent LIKE pattern injection.
+  # Escapes SQL LIKE wildcards (% and _) and limits query length.
+  #
+  # ## Examples
+  #
+  #     iex> sanitize_search_query("test%injection")
+  #     "test\\%injection"
+  #
+  #     iex> sanitize_search_query("very_long_search")
+  #     "very\\_long\\_search"
+  #
+  defp sanitize_search_query(query) when is_binary(query) do
+    query
+    |> String.slice(0, 100)
+    |> String.replace("\\", "\\\\")
+    |> String.replace("%", "\\%")
+    |> String.replace("_", "\\_")
+  end
+
+  defp sanitize_search_query(_), do: ""
+
   # ============================================================================
   # Search Filter Builders
   # ============================================================================
@@ -590,11 +618,13 @@ defmodule Mv.Membership.Member do
     if has_search do
       # Search query provided: return email-match OR fuzzy-search candidates
       trimmed_search = String.trim(search_query)
+      # Sanitize for LIKE patterns (contains uses ILIKE internally)
+      sanitized_search = sanitize_search_query(trimmed_search)
 
       # Build search filters - excluding custom_field_filter for performance
       fts_match = build_fts_filter(trimmed_search)
       fuzzy_match = build_fuzzy_filter(trimmed_search, @default_similarity_threshold)
-      email_substring_match = expr(contains(email, ^trimmed_search))
+      email_substring_match = expr(contains(email, ^sanitized_search))
 
       query
       |> Ash.Query.filter(