docs: reorganize tree, restore architecture + research from archive, add Phase 0 reports

Active docs/ was stub scaffolding while the real docs sat in docs/_archive/.
Restore and correct them, and record the Phase 0 work.

- docs/architecture/current.md: verified system map (from archived SYSTEM_OVERVIEW,
  9 corrections against code).
- docs/research/competitors.md: sourced competitor analysis (from archived
  PRODUCT_RESEARCH, feature matrix corrected).
- docs/decisions/ADR-002-job-application-model.md: the Job/JobApplication split.
- docs/application-discovery-report.md, docs/implementation-roadmap.md,
  docs/phase-0-foundation-report.md, docs/career-workspace-branch-assessment.md.
- Remove 10 zero-byte placeholder files that advertised content that never existed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/security/authentication.md

@@ -0,0 +1,84 @@
+# Authentication
+
+## Purpose
+
+Define user login and registration.
+
+---
+
+# Supported Methods
+
+Users should be able to:
+
+## Email Registration
+
+Create account using:
+
+- Email.
+- Password.
+- Confirmation.
+
+---
+
+## OAuth Registration/Login
+
+Support:
+
+- Google.
+- Microsoft.
+
+---
+
+# Expected Behaviour
+
+If OAuth user does not exist:
+
+Create account automatically.
+
+Example:
+
+User clicks:
+
+"Continue with Google"
+
+↓
+
+Authenticate
+
+↓
+
+No account exists
+
+↓
+
+Create account
+
+↓
+
+Login
+
+---
+
+# Password Requirements
+
+Support:
+
+- Secure hashing.
+- Password reset.
+- Password change.
+
+---
+
+# Authentication UX
+
+Users should have:
+
+- Clear errors.
+- Loading states.
+- Recovery options.
+
+Avoid:
+
+"Authentication failed"
+
+without explanation.