fix(installer): [UPD] stabilize web installer upgrade flow

[middleDuckAi]

Summary

• let loopback installer sessions recover instead of returning an opaque 404 after local cookie/session desync
• stop redefining EVO_MANAGER_PATH during install bootstrap
• bootstrap historical migrations_install entries before upgrade so existing SQLite installs do not rerun fresh schema creation
• guard missing HTTP_ACCEPT_LANGUAGE in installer language detection

Verification

• php -l on all touched installer/bootstrap files
• smoke-tested installer landing page on php -S with no warning output
• reproduced loopback lock takeover with POST /install/index.php?action=mode returning 200
• validated the migration-history bootstrap logic against the existing Evo SQLite upgrade shape