feat(devex): add a node quickstart example using the typescript sdk

[tiana-code]

E-09 DevEx #306 (F-09.7) - the examples directory, starting with one runnable quickstart.

What

examples/node-quickstart/ - a Node + TypeScript script that dogfoods the new @fincore/sdk-typescript (#305) via a file: dep:

• FincoreClient({ baseUrl: FINCORE_API_URL ?? localhost:8080, token: FINCORE_TOKEN }); listAccounts -> prints a summary + a row per account; getAccount(first) -> prints it.
• Base URL and bearer token come from the environment; nothing is hardcoded.
• package.json is private with no publish script.
• examples/README.md indexes the examples; node-quickstart/README.md documents starting the stack, building the SDK first, and the env vars.
• .github/workflows/examples-ci.yml (node 22) builds the SDK then typechecks + builds the example; it never starts a live stack.

This makes the SDK's value concrete and keeps the SDK honest (a real consumer compiles against it). More runtimes/examples are a natural follow-up.

Evidence (node v24 local)

Built the SDK, then example npm install (resolves the file: dep) + typecheck + build all green.

Gate chain

• code-reviewer: APPROVED, no must-fix - SDK API used exactly against source (no invented methods/fields), env-driven, CI builds the SDK before the example.
• security-auditor (opus): PASS, no must-fix - no hardcoded secrets (token from env only), §0 no-publish at package + CI layers, no live stack in CI, lockfile is devDeps + the file: SDK only with no postinstall, token never logged, clean-room clean, SPDX present.
• evaluator: PASS (0.89).
  Two LOW advisories declined with reason (node 22 matches the web-ci/sdk-ts-ci convention; npm install vs ci is intentional for the file:-linked dep).

Closes #306