[SCR-383] Auto-Mode (mode=auto) support

[kostas-jakeliunas-sb]

Merge order: part of the [SCR-383] Auto-Mode client rollout — merge once the server PR ScrapingBee/scrapingbee-API#1242 is merged + the flag is enabled.

tl;dr

Adds Auto-Mode (mode=auto) discoverability + docs to the Node SDK. The SDK is pass-through so the params already work on the wire today — this surfaces them for TypeScript autocomplete and documents the feature (including the under-documented spb-auto-cost response header). Version bumped 1.8.2 → 1.8.3, dist/ rebuilt and committed. 67 tests green.

Summary

• src/index.ts — added mode?: 'auto' and max_cost?: number to the HtmlApiParams type. Pure additive: the type's index signature ({ [key: string]: any }) already permitted these params, so no runtime change — this is for autocomplete/discoverability, consistent with how all other known params are enumerated.
• README.md — new "Auto-Mode" subsection in the HTML API section (after the GET example) with a htmlApi() GET example, a line showing how to read the credits charged via response.headers['spb-auto-cost'] (axios lowercases header keys — under-documented today), and caveats: GET only, max_cost optional (omit = uncapped), don't combine mode:'auto' with render_js/premium_proxy/stealth_proxy.
• CHANGELOG.md — added a 1.8.3 entry.
• package.json — version 1.8.2 → 1.8.3 (prebuild re-synced src/version.ts).
• dist/ — rebuilt committed output via npm run build (dist/index.d.ts has the new type fields; dist/version.{js,d.ts} reflect 1.8.3). dist/ is committed in this repo, so it's included in the PR.

Note: incidental package-lock.json churn from npm install (npm adding "peer": true annotations) was reverted to keep the diff focused — no dependency changes in this PR.

Client contract (server already shipped, beta, flag-gated)

• mode=auto: server tries cheap→expensive configs, stops at first success, charges only the winning config (0 credits if all fail).
• max_cost (int ≥ 1, optional, requires mode=auto): caps the credits a request may cost; omit = uncapped.
• Response header Spb-auto-cost = credits charged for the winning config.

Test plan

• npm install
• npm run build — prebuild syncs src/version.ts to 1.8.3, tsc compiles; dist/ updated and staged
• npm test — 67 passing (mocha + axios-mock-adapter, mocked; no network)
• Verified dist/index.d.ts contains mode?: 'auto' and max_cost?: number
• Verified package.json + src/version.ts + dist/version.{js,d.ts} all at 1.8.3
• Merge only after the server-side Auto-Mode feature is enabled in production

🤖 Generated with Claude Code