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/api-security.md

@@ -0,0 +1,40 @@
+# API Security
+
+## Requirements
+
+All APIs must:
+
+- Authenticate correctly.
+- Validate input.
+- Return safe errors.
+
+---
+
+# Rate Limiting
+
+Protect:
+
+- Login.
+- AI endpoints.
+- File uploads.
+- Public CV pages.
+
+---
+
+# API Keys
+
+Admin-only.
+
+Never expose:
+
+- Provider keys.
+- Secrets.
+- Tokens.
+
+---
+
+# External APIs
+
+Validate responses.
+
+Do not trust third-party data.