feat: store matching metadata on session file registration

Each saved file now records three additional fields:
  matched_identifier    — the literal animal_id_string or animal_name
                          substring that matched in the filename
  animal_id_string_snap — snapshot of animal.animal_id_string at
                          registration time
  animal_name_snap      — snapshot of animal.animal_name at
                          registration time

This lets future consumers (scripts, exports, re-matching) identify
the subject from the file record alone, even if animal data changes.
The matched identifier is also shown in the drop preview UI (↳ 2852).

Tests: 25 total (+2 for new payload fields).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/prisma/migrations/20250423010000_session_files_matching_metadata/migration.sql

@@ -0,0 +1,4 @@
+ALTER TABLE "session_files"
+    ADD COLUMN "matched_identifier"    TEXT,
+    ADD COLUMN "animal_id_string_snap" TEXT,
+    ADD COLUMN "animal_name_snap"      TEXT;

backend/prisma/schema.prisma

@@ -49,15 +49,18 @@ model DailyStatus {
 }
 
 model SessionFile {
-  id              String      @id @default(uuid())
-  daily_status_id String
-  daily_status    DailyStatus @relation(fields: [daily_status_id], references: [id], onDelete: Cascade)
-  filename        String
-  file_size       BigInt
-  file_type       String?
-  last_modified   BigInt?
-  notes           String?
-  created_at      DateTime    @default(now())
+  id                    String      @id @default(uuid())
+  daily_status_id       String
+  daily_status          DailyStatus @relation(fields: [daily_status_id], references: [id], onDelete: Cascade)
+  filename              String
+  file_size             BigInt
+  file_type             String?
+  last_modified         BigInt?
+  matched_identifier    String?     // the animal ID/name substring that matched in the filename
+  animal_id_string_snap String?     // snapshot of animal.animal_id_string at registration time
+  animal_name_snap      String?     // snapshot of animal.animal_name at registration time
+  notes                 String?
+  created_at            DateTime    @default(now())
 
   @@map("session_files")
 }

backend/src/routes/sessionFiles.js

@@ -2,7 +2,8 @@ const router = require('express').Router();
 const prisma = require('../lib/prisma');
 
 // POST /api/daily-statuses/:id/files  — register file metadata (batch)
-// Body: [{ filename, file_size, file_type, last_modified, notes }, ...]
+// Body: [{ filename, file_size, file_type, last_modified,
+//          matched_identifier, animal_id_string_snap, animal_name_snap, notes }, ...]
 router.post('/daily-statuses/:id/files', async (req, res, next) => {
   try {
     const status = await prisma.dailyStatus.findUnique({ where: { id: req.params.id } });
@@ -26,12 +27,15 @@ router.post('/daily-statuses/:id/files', async (req, res, next) => {
       files.map((f) =>
         prisma.sessionFile.create({
           data: {
-            daily_status_id: req.params.id,
-            filename:      f.filename.trim(),
-            file_size:     BigInt(Math.round(f.file_size)),
-            file_type:     f.file_type ?? null,
-            last_modified: f.last_modified != null ? BigInt(Math.round(f.last_modified)) : null,
-            notes:         f.notes ?? null,
+            daily_status_id:       req.params.id,
+            filename:              f.filename.trim(),
+            file_size:             BigInt(Math.round(f.file_size)),
+            file_type:             f.file_type             ?? null,
+            last_modified:         f.last_modified != null ? BigInt(Math.round(f.last_modified)) : null,
+            matched_identifier:    f.matched_identifier    ?? null,
+            animal_id_string_snap: f.animal_id_string_snap ?? null,
+            animal_name_snap:      f.animal_name_snap      ?? null,
+            notes:                 f.notes                 ?? null,
           },
         })
       )