feat(connectors): add easybill, GetMyInvoices and Billbee German connectors

[keysersoft]

Summary

Three new German/DACH marketplace connectors for high-adoption SaaS that lack a mature MCP server, all with documented public APIs. Selected via deep research over German software with public APIs and no existing MCP, excluding the 31 connectors already in the catalog.

Connector	Category	API	Auth
easybill	invoicing/accounting	REST v1	Bearer token
GetMyInvoices	invoice/document mgmt	REST v3	X-API-KEY header
Billbee	multichannel order mgmt	REST v1	Basic Auth + X-Billbee-Api-Key

Verification

• validate-adapters.mjs: 183/183 pass, 0 errors, 0 warnings on the new adapters.
• Each connector ships a *.live.spec.ts with always-on static conformance checks (base URL, auth scheme, documented paths) + opt-in live edge-reachability checks (RUN_<NAME>_LIVE).
• Endpoint paths and auth schemes were probed against the live vendor APIs.
• GetMyInvoices verified end-to-end with a real key (pagination envelope + companies array confirmed); also caught and fixed a real bug — updatedOrNewSinceFilter requires Y-m-d H:i:s, not a plain date (the API returns 422 otherwise).

Notes

• easybill and Billbee data-level e2e pending valid credentials (per-user runtime env vars; connector code is correct and ships independently).