fix(zapier): address review feedback (masked key, ES imports) + test hygiene

- authentication: API key field is now type 'password' so Zapier masks it in
  the connection UI instead of showing it in cleartext.
- index: use ES imports for the platform version and package version instead of
  require(), matching the repo's TypeScript rule. dist stays flat; both versions
  resolve at runtime.
- AGENTS.md: add the Key Directories row for integrations/zapier-mem0.
- tests: disable telemetry during test runs so CI never fires real PostHog
  events, which also removes a lingering open handle after the suite.

Verified: build + zapier validate (0 failures) + 16 tests (13 unit, 3 live E2E).

integrations/zapier-mem0/test/setup.ts

@@ -0,0 +1,3 @@
+// Disable telemetry during tests so runs never fire real PostHog events
+// (and so the fire-and-forget fetch cannot leave an open handle after tests).
+process.env.MEM0_TELEMETRY = 'false';