refactor(runtime): remove disabled validation and overlay code

[Alx8g]

Summary

• remove disabled adaptive gameplay validation and unreachable IPC/persistence glue
• remove the already-unshipped performance/network overlay implementation
• remove six definition-only exports and dead overlay theme variables
• remove two unreferenced repository images
• add a CSS fallback that hides Krunker's Live Streams self-promotion while preserving real streams

Size impact

• 2,686 lines removed
• JavaScript outputs reduced from 16 to 13
• shipped JavaScript reduced by 38,294 bytes
• packaged ASAR reduced by 40,259 bytes in the local comparison

Preserved

• legacy profile and URL migration
• old Competitive Mode backup restoration
• environment-gated performance probes
• launch videos and weapon morph presentation

Validation

• pnpm run validate: 579 tests passed
• pnpm run bundle:verify: 26 outputs verified
• TypeScript no-unused locals/parameters check passed
• package inventory and 17/17 default runtime payload comparison passed
• Windows smoke test passed; real streams remained and self-promotion was absent