docs: clean up ADR-005 architecture docs after envelope implementation

Remove stale ADR-005 drift tables across all architecture docs since
ResponseEnvelope types, factories, detection, and integration points
are now fully implemented in source code. Key changes:

- api-surface.md: Remove ADR-005 drift table (all items implemented),
  retain ADR-006 drift table without execute() return type (now done)
- call-protocol.md: Remove ADR-005 drift table, update ADR-006 table,
  fix CallHandlerConfig to show callMap? (current source)
- adapters.md: Remove 'current source state' and 'implementation
  changes needed' tables for from_mcp and from_openapi, replace with
  current-accurate descriptions of envelope behavior
- response-envelopes.md: Remove 'current source state' blocks,
  update migration checklist to show all code changes completed
- 005-response-envelopes.md: Change status from Draft to Implemented
- 006-unified-invocation-path.md: Update Prerequisites section to note
  ADR-005 is now implemented
- build-distribution.md: Add response-envelope.ts to source layout
- architecture.md: Add response-envelopes.md link and ADR-005/006
  entries to design decisions table
- README.md: Add response-envelopes.md to documents table
- Update last_updated dates on all changed docs

docs/architecture/README.md

@@ -1,6 +1,6 @@
 ---
 status: draft
-last_updated: 2026-05-09
+last_updated: 2026-05-11
 ---
 
 # @alkdev/operations Architecture
@@ -74,6 +74,7 @@ Spokes will import `@alkdev/operation` for operation definitions and `@alkdev/pu
 |----------|---------|
 | [api-surface.md](api-surface.md) | All public types, registry, call protocol, subscribe, env, adapters |
 | [call-protocol.md](call-protocol.md) | PendingRequestMap, CallHandler, call≡subscribe, events, error model, access control |
+| [response-envelopes.md](response-envelopes.md) | Response envelope types, factory functions, detection, schemas, integration points |
 | [adapters.md](adapters.md) | from_schema, from_openapi, from_mcp, scanner — how they work, how to add new adapters |
 | [build-distribution.md](build-distribution.md) | Dependencies, project structure, sub-path exports, peer deps, build tooling |