Document canonical runtime bundle suite (e2e/trap/parity) #5

Cross-repo onboarding task (good first issue).

Scope:

• Add a short docs page that explains the canonical runtime bundle suite in t81-examples:
  • run-runtime-v0.5-e2e.sh
  • run-runtime-v0.5-trap-diagnostics.sh
  • run-runtime-v0.5-mode-parity.sh
• Link the page from existing runtime contract docs navigation.

Definition of done:

• page committed in t81-docs
• links to all three bundle scripts
• references active baseline runtime-contract-v0.5
• one CI run URL included in PR description