feat(connectors): callApi for metered connectors

[ChenMachBase]

Summary

Adds callApi / callWorkspaceApi / callCurrentAppUserApi for metered connectors — connectors backed by paid third-party APIs that charge Base44 per call.

For those connectors the OAuth token is deliberately unavailable to app code (getConnection and friends reject with a 403), because the Base44 proxy is the only place the calls we pay for can be counted. These three methods are the replacement, and each mirrors its getConnection counterpart so the identifier you already use carries over:

New method	Replaces	Identified by
callApi(integrationType, request)	getConnection	integration type
callWorkspaceApi(connectorId, request)	getWorkspaceConnection	connector ID
callCurrentAppUserApi(connectorId, request)	getCurrentAppUserConnection	connector ID

const res = await base44.asServiceRole.connectors.callApi('x', {
  method: 'POST',
  path: '/2/tweets',
  body: { text: 'Shipped!' },
});
// -> { success, status, data, headers, creditsCharged }

Two shape decisions worth reviewing

An upstream 4xx/5xx resolves, it does not throw. A provider error is a normal outcome of a call Base44 completed and billed, so it comes back as success: false with the provider's own status and data. Only Base44-side failures — no connection, credits exhausted, a rejected request — reject the promise. Tests pin both sides of that split.

query is always forwarded, never dropped. The server prices the merged query string, so an SDK that accepted the field and then discarded it would make the quoted price and the real request disagree. (This is the client-side half of a billing bypass caught during review of the backend change.)

Responses carry creditsCharged, and the module docs gain a "Metered connectors" section noting that cost can vary by two orders of magnitude between endpoints on the same connector — an expensive call inside a loop being the failure mode worth warning about.

Testing

• 11 new unit tests in tests/unit/connectors-proxy.test.ts: route targeting per connector kind, payload normalization, snake_case → camelCase mapping, query forwarding, upstream-error-resolves vs Base44-error-rejects, and the metered 403 surfacing an actionable message.
• Full suite green: 203 tests, plus tsc --noEmit, npm run test:types, and eslint src all clean.
• Installed with npm ci (lockfile-exact).

Notes

• No version bump. Publishing, and bumping the pinned npm:@base44/sdk@0.8.40 in the platform's builder prompts, is a separate release step — that pin touches several prompt files including system-prompt ones, so it wants its own change.
• Backend counterpart: base44-dev/apper#19753. That PR ships inert (no connector is registered as metered yet), so nothing here is load-bearing until it is.
• Opened from a fork because the author's account has read-only access to this repo.