feat: mark glossary templates as multilingual — support 11 target languages

Templates enriched by enrich_glossary_templates.py already contain
translations for de, es, it, pt, nl, ru, ja, ko, zh, ar, fa (including
Persian). But they were labeled FR→EN, causing incorrect filtering and
warnings when translating to other languages.

Changes:
- index.json: set target_lang='multi' for all 8 templates
- GlossarySelector: treat target_language='multi' as compatible with
  any target language (no false warnings, auto-select works)
- GlossarySelector: display '🌐 MULTILINGUE' badge instead of EN flag
- glossary_routes: default target_language to 'multi' instead of 'en'
- Migration: detect existing multilingual glossaries in DB (5+ keys in
  translations JSON) and set their target_language to 'multi'

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

alembic/versions/a1b2c3d4e5f6_set_multilingual_target_language.py

@@ -0,0 +1,54 @@
+"""Set multilingual glossaries target_language to 'multi'
+
+Revision ID: a1b2c3d4e5f6
+Revises: e5b2c9d1f4a8
+Create Date: 2026-05-31
+
+Glossary templates that were enriched with multilingual translations
+(via enrich_glossary_templates.py) contain translations for 11 languages
+(de, es, it, pt, nl, ru, ja, ko, zh, ar, fa) in each term's translations
+field. These should be marked as target_language='multi' instead of 'en'.
+
+This migration detects glossaries whose terms have multilingual translations
+and sets their target_language to 'multi'.
+"""
+
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers
+revision = "a1b2c3d4e5f6"
+down_revision = "e5b2c9d1f4a8"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # Glossaries with terms containing 5+ translation keys are multilingual templates
+    # (enriched glossaries have 11 translations: de, es, it, pt, nl, ru, ja, ko, zh, ar, fa)
+    op.execute("""
+        UPDATE glossaries
+        SET target_language = 'multi'
+        WHERE id IN (
+            SELECT DISTINCT g.id
+            FROM glossaries g
+            JOIN glossary_terms gt ON gt.glossary_id = g.id
+            WHERE gt.translations IS NOT NULL
+              AND jsonb_typeof(gt.translations) = 'object'
+              AND (
+                SELECT count(*)
+                FROM jsonb_object_keys(gt.translations)
+              ) >= 5
+        )
+    """)
+
+
+def downgrade() -> None:
+    # Revert multilingual glossaries back to 'en'
+    op.execute("""
+        UPDATE glossaries
+        SET target_language = 'en'
+        WHERE target_language = 'multi'
+    """)