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/architecture/authentication.md

@@ -0,0 +1,48 @@
+# Authentication Architecture
+
+## Supported Methods
+
+Email/password.
+
+Google OAuth.
+
+Microsoft OAuth.
+
+
+---
+
+# Future
+
+Potential:
+
+Other providers.
+
+Enterprise login.
+
+---
+
+# Requirements
+
+Authentication should support:
+
+- Registration.
+- Login.
+- Password reset.
+- 2FA.
+- Account management.
+
+---
+
+# User Creation
+
+OAuth users:
+
+If account does not exist:
+
+Create automatically.
+
+---
+
+# Separation
+
+Authentication identity != career profile.