This PR changes the SDK's wire TypeScript types to be generated from the Rust
wire model by a hand-written emitter (no third-party generator), guarded by a
conformance test and a CI gate so they cannot drift, and retires the
hand-maintained 0.5.0-alpha-strict stable schema view. This closes the third
versioning drift surface: a wire-model change ripples to the Rust model, the JSON
schema, and the SDK types, or it fails CI.

Details:
- Add wxc_common::ts_emit, a Rust emitter that walks the generated schema value
  and emits TypeScript (string-union enums, closed/open objects, $ref,
  anyOf [T, null], arrays, scalars). Refactor wire.rs so the JSON-schema renderer
  and the new generate_sdk_types_ts() share a schema_value() helper; the JSON
  schema output stays byte-for-byte identical.
- Add a --ts mode to mxc_schema_gen that emits the committed
  sdk/src/generated/wire.ts (an internal drift oracle, not public API).
- Add sdk/tests/unit/wire-conformance.test.ts: compile-time assertions that
  sdk/src/types.ts conforms to the generated wire shape - bidirectional and exact
  (public/wire field rename/removal, wire-only field additions, and enum
  narrowing and widening), at the root and every leaf, with each intentional
  divergence pinned to a documented allow-list.
- Add scripts/versioning/check-sdk-types-codegen.js, a CI gate that runs the
  emitter and diffs the committed wire.ts (mirrors check-schema-codegen.js); wire
  it into the Versioning Checks job. No new npm or cargo dependency.
- Retire schemas/stable/mxc-config.schema.0.5.0-alpha-strict.json and update the
  doc references (sdk/README.md, docs/schema-codegen.md, copilot-instructions.md).

Tests:
- cargo test --workspace; cargo fmt --all -- --check; cargo clippy --workspace
  --all-targets -- -D warnings; ts_emit unit tests.
- Schema codegen, SDK wire-types codegen, and config corpus (169/169) gates.
- cd sdk && npm test.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Generated-with: claude-opus-4.8

…atives)

This PR addresses two review comments from bbonaby on the 2C PR (#559):

Details:
- Reword the header comment in check-sdk-types-codegen.js to drop the internal
  "Phase 2C, option C" / "options A/B" vocabulary, matching the repo convention
  of keeping phase/spike naming out of shipped files. It now just describes what
  the gate does.
- Add an "Alternatives considered" subsection to docs/schema-codegen.md
  explaining why the SDK wire types use a hand-written Rust emitter (drift
  oracle) rather than generating the public API directly or using a third-party
  schema->TS generator, plus a note on the FlatBuffers option. Makes the
  rationale discoverable for future readers.

Tests:
- node scripts/versioning/check-sdk-types-codegen.js (gate still green;
  docs/comment-only change, generated wire.ts unaffected).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Generated-with: claude-opus-4.8