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/principles.md

@@ -0,0 +1,46 @@
+# Architecture Principles
+
+## 1. Keep Business Logic Separate
+
+Business rules should not live inside:
+
+- Controllers.
+- React components.
+- Database models.
+
+---
+
+# 2. Single Responsibility
+
+Classes and components should have one purpose.
+
+---
+
+# 3. Prefer Composition
+
+Create reusable services.
+
+Avoid giant classes.
+
+---
+
+# 4. Backwards Compatibility
+
+Existing functionality should continue working during migrations.
+
+---
+
+# 5. Explicit Over Clever
+
+Readable code is preferred over complex abstractions.
+
+---
+
+# 6. Test Important Logic
+
+Prioritise testing:
+
+- Business rules.
+- AI workflows.
+- Document generation.
+- Authentication.