ENG-4669 Capture all signups for Infisical Cloud

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Greptile Summary

This PR adds HubSpot CRM integration to capture signup events on Infisical Cloud, wiring two new signup flows (email account completion and invite-based account completion) into a new sendHubSpotSignupEvent telemetry call. The integration is correctly gated behind isProductionMode, InstanceType.Cloud, and both HubSpot env vars being present, consistent with the existing sendLoopsEvent pattern.

Key changes:

• Two new optional env vars (HUBSPOT_PORTAL_ID, HUBSPOT_SIGNUP_FORM_ID) added to opt into the integration
• New sendHubSpotSignupEvent function in the telemetry service that POSTs to the HubSpot Forms v3 API with email, signup method, and optional name fields built dynamically via a loop
• authMethod is now surfaced from completeEmailAccountSignup's return value and forwarded to HubSpot; the invite flow uses the hardcoded literal "invite"
• Minor: the HubSpot submission context always records pageUri as …/signup and pageName as "App Signup" regardless of which flow triggered the event, causing invite-based completions to be misattributed in HubSpot analytics

Confidence Score: 4/5

• This PR is safe to merge; the integration is well-guarded and failures are non-blocking.
• The implementation is solid: previous review concerns (missing isProductionMode guard and static field construction) have been addressed. The only outstanding issue is a minor analytics accuracy concern where the hardcoded pageUri/pageName in the HubSpot context misattributes invite-based account completions to the direct signup page in HubSpot reporting. This does not affect correctness or security of the signup flow itself.
• backend/src/services/telemetry/telemetry-service.ts — the hardcoded HubSpot submission context (pageUri/pageName) affects analytics attribution accuracy for invite completions.

Important Files Changed

_{Last reviewed commit: "Merge remote-trackin..."}

@greptile please check the latest changes and re-check this PR, also update the Greptile Summary