Maya signs in to access form authoring

[danielnaab]

User Story:

As a form creator (Maya), in order to securely access form authoring tools, I want to sign in with my GitHub account and see authoring options that anonymous visitors cannot

Preconditions:

• Skeleton complete (Slice 0)
• GitHub OAuth application configured

Acceptance Criteria:

• Sign-in link visible on public pages
• Clicking sign-in initiates GitHub OAuth flow
• After authentication, user sees their identity (name/avatar) in the header
• Authenticated users see authoring navigation (e.g., "My Projects", "Upload Form")
• Unauthenticated users see only public catalog content
• Sign-out clears the session
• Auth middleware protects authoring routes, redirects to sign-in

Success Metrics:

• Authentication round-trip completes in under 3 seconds
• Protected routes correctly reject unauthenticated requests

Notes:

• Authorization model: GitHub repo write access = authoring permission (can be simplified for MVP)
• Session storage: cookie-based, server-side session
• Public routes: /, /catalog/*, /health
• Protected routes: /authoring/*, future upload/edit routes
• This slice does NOT include any form authoring functionality — just the auth gate

Definition of Done:

• Acceptance criteria met
• Threat model updated -- any new trust boundaries, data flows, or attack surfaces are reflected in catalog/architecture/threat-model.md
• Technical documentation updated -- architecture docs and decisions are current
• Tests pass including auth middleware tests
• Type checking passes
• CI pipeline green
• Deployed and demoable

[danielnaab]

All acceptance criteria verified as met: sign-in link on public pages, GitHub OAuth flow, identity in header, authoring nav for authenticated users, public-only content for anonymous users, sign-out clears session, auth middleware protects routes with redirect.