test: add build smoke tests for ESM, CJS, and TypeScript exports

[OlaGreat]

Summary

Source tests import directly from src/, so they can pass even when the built package's exports are broken. This PR adds smoke tests that exercise the actual dist/ output the way a real consumer would, plus wires them into CI right after the build step.

• tests/smoke/esm.smoke.mjs — imports dist/index.mjs (native ESM) and exercises GuildPassClient, GuildPassError, GuildPassErrorCode, and several utility/config exports, asserting both shape and runtime behaviour (client wiring, error codes).
• tests/smoke/cjs.smoke.cjs — require()s dist/index.js (CommonJS) and runs the same checks.
• tests/smoke/types.smoke.ts + tsconfig.smoke.json — a compile-only (noEmit) TypeScript check that imports types from the built dist/index.d.ts (not src) and verifies they resolve and type-check correctly. skipLibCheck is explicitly disabled for this check only, since the whole point is to validate the declaration file itself — leaving it on (as the base tsconfig.json does) would silently skip the exact errors we're trying to catch.
• A new test:smoke script runs all three checks in sequence: node tests/smoke/esm.smoke.mjs && node tests/smoke/cjs.smoke.cjs && tsc -p tsconfig.smoke.json.
• .github/workflows/ci.yml runs pnpm test:smoke as a new step immediately after pnpm build.
• tsconfig.json now excludes tests/smoke from the main project compile, since those files reference dist/*, which doesn't exist yet when pnpm typecheck runs (before the build step) in CI.

Bug found and fixed while building this

Writing the smoke tests surfaced a real, pre-existing issue: package.json#exports listed conditions in the order require, import, types. tsup/esbuild explicitly warns that this ordering means the types condition can never be reached, since require/import match first for their respective resolution contexts. The conventional and correct order is types first, so resolvers checking the condition map find it before falling through to a module condition. Fixed by reordering to types, require, import. After the fix, pnpm build no longer emits the exports-order warning.

Verification

I manually verified the smoke tests actually catch breakage (not just "always green"):

• Stripped an export out of the built dist/index.mjs → node tests/smoke/esm.smoke.mjs fails with a clear SyntaxError: ... does not provide an export named ... and a non-zero exit code.
• Renamed a class inside dist/index.d.ts → tsc -p tsconfig.smoke.json fails with TS2304: Cannot find name 'GuildPassClient' and a non-zero exit code.

Also ran the full existing pipeline locally to confirm no regressions: pnpm lint, pnpm typecheck, pnpm test:run (20/20 passing), pnpm build, pnpm test:smoke — all green.

Test plan

• pnpm install
• pnpm typecheck — passes (smoke files excluded pre-build, as expected)
• pnpm test:run — 20/20 unit tests pass
• pnpm build — no exports-order warning
• pnpm test:smoke — ESM import, CJS require, and type-check all pass against dist/
• Confirmed each smoke check fails loudly when the corresponding export/type is broken (see Verification above)
• CI run on this PR (will run automatically)

Closes #23