feat(forms): HubSpot lead capture + Pages deploy workflow (closes #7)

[FabioLeitao]

Summary

• Removes silent preventDefault on demo and login forms.
• Demo form (agende-demonstracao.html) posts to HubSpot's public form submit API via js/forms.js.
• portalId / formGuid are written to js/form-config.js at deploy time from GitHub Actions secrets — no private API keys in the repo.
• Until secrets are set, visitors see a clear mailto fallback (contact@databoar.com.br).
• Login form shows an "em breve" message (no credential handling until product SSO exists).
• Adds docs/HUBSPOT_SETUP.md and .github/workflows/pages-deploy.yml.

Operator follow-up (not in this PR)

1. Repo Settings → Secrets: HUBSPOT_PORTAL_ID, HUBSPOT_DEMO_FORM_GUID, optional HUBSPOT_REGION
2. Settings → Pages → Source: GitHub Actions (replaces branch-only publish so secrets inject at deploy)
3. Align HubSpot form fields per docs/HUBSPOT_SETUP.md

Test plan

• Without secrets: submit demo form → info message with mailto fallback
• With secrets + Actions deploy: submit creates HubSpot contact
• Login submit → em breve message, no network call
• No API keys in git diff

Partial for/id on demo + login fields (full #2 sweep can follow).

Closes #7

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