Remove billing email types and SendGrid integration

[BrewingCoder]

Parent: #25 — Remove all SaaS billing code

Depends on: #26 (SendBillingNotifications removal)

What to Remove

email/email.go

• 18 billing email type constants (lines 36-53): BillingHighlightTrial7Days through BillingInvalidPayment
• OneTimeBillingNotifications array (lines 56-62)
• getBillingNotificationSubject() function (lines 151-192)
• getBillingNotificationMessage() function (lines 194-257)
• SendBillingNotificationEmail() function (lines 259-294)
• BillingNotificationTemplateID constant (line 25)
• SendGridOutboundEmail constant (line 27) — if only used by billing

main.go — SendGrid client initialization

Line	Usage
59	Import: sendgrid
364	sendgrid.NewSendClient(env.Config.SendgridKey)
500, 585	Passed to worker/OTEL resolvers

Resolver MailClient fields

File	Line	Usage
public-graph/graph/resolver.go	87	MailClient *sendgrid.Client
private-graph/graph/resolver.go	134	MailClient *sendgrid.Client

env config

• SendgridKey env var — may need to keep if SendGrid is used for non-billing emails

Strategy

Check if SendGrid/email is used for ANY non-billing purpose. If billing is the only email use case, the entire email package + SendGrid dependency can be removed.

Test Plan

• Determine if non-billing emails exist
• Remove billing email types and functions
• Remove or simplify SendGrid initialization
• Remove MailClient from resolvers if fully unused
• Verify build + tests

🤖 Generated with Claude Code

[github-actions]

AI Triage: Remove billing-related email types, SendGrid integration, and associated code as part of SaaS billing removal.

Labels applied: area:backend, tech-debt, billing-removal, priority:medium, component:graphql