fix: preserve legacy deletion flows

[ackness]

Summary

• keep pre-incarnation player sessions deletable after in-place upgrades without weakening current session-generation isolation
• confirm world and session deletion with Enter while preventing repeat submission during deletion
• render the delete confirmation from both the world list and world detail view

Verification

• pnpm --filter @covel/server test (105 files passed, 830 tests passed, 2 files/16 tests skipped)
• pnpm --filter @covel/web test (111 files passed, 693 tests passed)
• pnpm --filter @covel/server lint
• pnpm --filter @covel/web lint
• pnpm check:i18n
• commit hooks, including root pnpm lint

Release context

Required before creating the v0.0.28 tag. The tag has not been created yet.