[P3-10] npm publish wiring for @codegraff/sdk@0.2.0 (sdk-v* tag → matrix → publish)

[justrach]

Parent: #34
Priority: P3 (release gate — graff-agent can't npm install until this lands)
Branch base: release/0.1.53

Why

.github/workflows/sdk-typescript.yml builds the cross-platform binary matrix and assembles npm subpackages, but stops at the inspection step. graff-agent depends on @codegraff/sdk from npm, so we need to wire the publish step.

Scope

• Add a publish job to .github/workflows/sdk-typescript.yml that:
  • Runs after assemble.
  • Triggers only on tag push matching sdk-v* (separate tag namespace from binary releases).
  • Runs napi prepublish then npm publish --access public for each sdk/typescript/npm/<triple> subpackage.
  • Finally publishes the root @codegraff/sdk package.
• Document the release flow in sdk/typescript/RELEASING.md.
• First release: @codegraff/sdk@0.2.0 once items P0-1 through P2-9 are merged.

Acceptance

• Tag sdk-v0.2.0-rc.1 pushes successfully publishes a release-candidate to npm
• npm install @codegraff/sdk@0.2.0-rc.1 from a fresh dir installs the right platform binary
• RELEASING.md covers tag, publish, and rollback procedures