Add io.pilot.primitive (Primitive — email for AI agents) + emailless signup scaffold step

[Alexgodoroja]

What

Publishes io.pilot.primitive — Primitive, programmatic email infrastructure for AI agents — and adds the small scaffold feature it needs.

Scaffold: create signup step + free-plan help disclaimer

• New no-broker signup step create: a single unauthenticated POST (static body, e.g. {terms_accepted:true}) that mints the API key and caches it — plus the provisioned inbox address — to $APP/secrets.json in one call. No email, no OTP, no broker. Complements the existing register/verify/broker/account steps.
• requireKey preflight: an unauthenticated call soft-fails with exact activation instructions (call the signup method) instead of a raw 401. Once minted, the key is injected on every request via the byo ${TOKEN} header — the agent never handles it.
• Methods can declare a gated reason; the generated <ns>.help renders those under a NOT AVAILABLE ON THE FREE PLAN disclaimer at the bottom of the output.
• Mirrored across scaffold.Config, the publish.Submission model, validation, and ToConfig. New test TestCreateSignupGrantsAndCompiles (generates + compiles + checks grants/soft-fail/disclaimer).

Submission: submissions/io.pilot.primitive/submission.json

• 110 methods over one byo HTTP backend (Authorization: Bearer ${PRIMITIVE_API_KEY}).
• primitive.signup provisions a free account + managed *.primitive.email inbox in one call; every other method authenticates automatically.
• 57 reachable on the free agent plan (account, inbox, domains, send/reply/batch, inbox listing/search/get/raw/attachments/conversation, threads, filters, endpoints, memories, webhook deliveries); 52 marked gated (Functions, Wake, x402 payments, custom domains, recipient routes, semantic search) — implemented and callable, labeled in help until the account is upgraded.

Testing

• verify-submission → VERIFY OK (scaffolds + cross-compiles all 4 platforms + catalogue gate).
• Full e2e in socket mode against live primitive: soft-fail → signup → key auto-injected → account/status reads, send A→B (SMTP 250), inbound list/get/conversation/raw/search, threaded reply via send_email, memories set/get/search/delete, filters + endpoints CRUD. Zero adapter bugs; gated families return the expected plan/entitlement errors.
• go build ./... && go vet ./... && go test ./... all green; gofmt clean.