feat: add conditional SQLITE/EXTDB blocks to app.ini template

Phase scripts strip the irrelevant block after render_template:
sqlite3 removes EXTDB_BLOCK, external DBs remove SQLITE_BLOCK.

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

templates/app.ini.tpl

@@ -13,7 +13,15 @@ LFS_START_SERVER = true
 
 [database]
 DB_TYPE = ${GITEA_DB_TYPE}
+; SQLITE_BLOCK_START
 PATH    = /data/gitea/gitea.db
+; SQLITE_BLOCK_END
+; EXTDB_BLOCK_START
+HOST    = ${GITEA_DB_HOST}:${GITEA_DB_PORT}
+NAME    = ${GITEA_DB_NAME}
+USER    = ${GITEA_DB_USER}
+PASSWD  = ${GITEA_DB_PASSWD}
+; EXTDB_BLOCK_END
 
 [security]
 INSTALL_LOCK = true