Phase 4: docs and ADRs - supersede 0001/0002, update the glossary, add-an-endpoint checklist

[SyniRon]

Parent

Part of #112 (PRD: Goodbye gRPC) — Phase 4 (Delete).

What to build

The documentation close-out:

• New ADR recording why the split-process design was retired: zero measured external gRPC traffic, the single-listener rewrite, the golden-enforced contract. Supersedes ADR 0001 (split process) and ADR 0002 (intra-process plaintext dial). (ADR 0003 was superseded back in Phase 2; ADR 0004 scope-auth is unchanged.)
• Domain glossary (CONTEXT.md) updated: "the proto files are the contract" now points at the types package, the golden-validated OpenAPI 3.1 spec, and the golden corpus. The Keycloak chopping-block note becomes past tense. The wire conventions (lowerCamelCase, emit-everything, 64-bit-as-string, enum names) get recorded as house style for future endpoints.
• Contributor add-an-endpoint checklist: struct → handler → route registration → spec operation → goldens, with a note that the spec steps are CI-enforced (drift fails naming the operation and field — no tribal knowledge required).
• Swagger 2.0 retirement executed per the codegen question's answer (full retirement, or a frozen alias kept alongside).
• Optional cosmetic: the single-file modern docs renderer swap (URLs unchanged). The docs friendliness pass stays out of scope.

Acceptance criteria

• ADR landed; 0001/0002 marked superseded
• CONTEXT.md reflects the new contract trio + house style
• Add-an-endpoint checklist in contributor docs
• 2.0 retirement decision executed and recorded

Blocked by

• Phase 4: delete the gRPC server, gateway, proto/buf toolchain, second port, and CI codegen #135 — the deletion this documents
• Question: does any consumer generate client code from the served swagger.json? #117 — the codegen answer