migrate Nextcloud from SQLite to MySQL InnoDB Cluster

SQLite was causing constant crash-looping (138 restarts/day) due to
write lock contention with concurrent sync clients.

Migration required workarounds for multiple occ db:convert-type bugs:
- GR error 3100: SET GLOBAL sql_generate_invisible_primary_key = ON
- utf8mb3 column creation: stripped 4-byte emoji + invalid UTF-8 from
  SQLite (F1 calendar events, filecache)
- SQLite index corruption: repaired via .dump + INSERT OR IGNORE reimport
- kubectl exec timeouts: used nohup + detached process

Verified: all 136 tables migrated, 100% row count match across 15 key
tables (users, files, calendars, contacts, shares, activity).

Also fixed typo: databse → database in chart values.

stacks/nextcloud/chart_values.yaml

@@ -40,21 +40,20 @@ nextcloud:
       mountPath: /etc/apache2/mods-available/mpm_prefork.conf
       subPath: mpm_prefork.conf
 
-# internalDatabase:
-#   enabled: false
+internalDatabase:
+  enabled: false
 
 externalRedis:
   enabled: true
   host: ${redis_host}
 
-# Currently not in use; we use the nextcloud.db sqlite3
 externalDatabase:
-  enabled: false
+  enabled: true
   type: mysql
   host: ${mysql_host}
   user: nextcloud
   password: ${db_password}
-  databse: nextcloud
+  database: nextcloud
 
 persistence:
   enabled: true