feat(wizard): optional AcoustID key step for metadata enrichment

Adds a wizard step (after the ML step) that prompts for an AcoustID API
key. Left blank, enrichment runs on embedded tags only; with a key the
backend also identifies untagged files by audio fingerprint (§1D). The
key is appended to .env.deploy and reaches both api and worker via
env_file. en/ru strings included.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/env_gen.sh

@@ -75,5 +75,14 @@ generate_env() {
         } >>"$ENV_FILE"
     fi
 
+    # -- optional AcoustID key (metadata enrichment §1D) ------------------
+    if [[ -n "${CFG_ACOUSTID_KEY:-}" ]]; then
+        {
+            echo ""
+            echo "# -- metadata enrichment (AcoustID) -------------------------------------"
+            echo "ACOUSTID_API_KEY=${CFG_ACOUSTID_KEY}"
+        } >>"$ENV_FILE"
+    fi
+
     chmod 600 "$ENV_FILE"
 }