docs(specs): establish protocol terminology

[Wondertan]

Summary

This PR establishes the protocol vocabulary and system model used by the ceremony specification. It is stacked on #20 so its naming choices can be reviewed without delaying the protocol changes.

Changes

Application and integration roles

• Define Application and Application Deployment for the user-facing product and its frontend, backend, OAuth-client, redirect, and proving infrastructure.
• Define Identity Integrator as the party that deploys or maintains an Identity Integration.
• Rename the chain-side Consumer to Identity Integration.

Ledger and verification roles

• Rename Consumer Chain to Execution Ledger.
• Rename Chain ID, chainId, and Chain Profile to Ledger ID, ledgerId, and Ledger Profile.
• Rename the shared Proof Verifier to Verifier Dispatcher.
• Rename each ledger-specific platform verifier to Ledger OAuth Platform Proof Verifier (LOPPV); the implementation-neutral selector remains Platform Ceremony Version.

Browser and proof terms

• Rename Canonical Runtime to Ceremony Client and Redirect Runtime to Ceremony Popup.
• Rename the verifier input from Submission to OAuth Proof, distinguishing it from both the Execution Ledger transaction and the zero-knowledge proof.
• Update the system diagram, role tables, assumptions, requirements, tests, and security prose to use those terms consistently.

Scope

This is a naming and system-model change. It does not change nonce construction, ceremony lifecycle, proof delivery, platform endpoints, or verifier behavior.

Validation

• git diff --check
• Old-term consistency search across all three normative files

[Wondertan]

This is still wanted and awaits until protocol settles so we can rename everything at once