feat(apiserver): give the WhatsApp/Email autopilot enough loan context to answer basic questions

[psanders]

Summary

Answers a question that came up while testing: does the WhatsApp agent have loan context available to it? Short answer — the data was already loaded, but almost none of it was reaching the model.

• buildOutreachContext already pulls the full account/loan record (principal, terms, balance, days past due, missed installments, last payment, etc.) into EmailAutopilotRequest.context.
• But buildPrompt() in both whatsAppAutopilot.ts and emailAutopilot.ts only ever converted two fields into actual prompt text: outstandingBalance, and a customerName key that buildOutreachContext never sets (it's firstName/fullName) — so that line silently never rendered. In practice the model had the balance and nothing else, and couldn't answer "when's it due" / "what are my terms" / "did I miss a payment" even though the answer was sitting in the DB the whole time.
• New buildAutopilotContextLines (mods/common/src/utils/outreach.ts), shared by both autopilots instead of each hand-rolling its own copy — the customerName/firstName mismatch is exactly the kind of drift duplicating this invites. Surfaces principalAmount, termsAmount/termsFrequency/termsLength, daysPastDue, missedInstallments, lastPaymentDate/lastPaymentAmount, each only when meaningful for the account (e.g. skips "días de atraso" when the account isn't past due).
• Deliberately excludes negotiationOptions — internal, freeform admin notes on negotiation flexibility (e.g. discount thresholds), not safe for the model to repeat verbatim to a customer. Covered by a regression test asserting it never leaks into the context lines.
• Added one instruction line telling the model it may use the Contexto to answer basic loan questions and not invent data outside it.

Test plan

• npm test --workspace=mods/common — 132 passing (128 existing + 4 new, incl. the negotiationOptions exclusion check)
• npm test --workspace=mods/apiserver — 230 passing (no regressions)
• npm run typecheck — common + apiserver clean
• eslint on changed files — clean

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