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/database.md

@@ -0,0 +1,78 @@
+# Database Architecture
+
+## Principles
+
+The database represents business concepts.
+
+---
+
+# Core Entities
+
+## User
+
+Account information.
+
+---
+
+## Job
+
+A job opportunity.
+
+---
+
+## Application
+
+User's application to a job.
+
+---
+
+## Company
+
+Organisation.
+
+---
+
+## Career Profile
+
+Professional identity.
+
+---
+
+## CV
+
+Generated documents.
+
+---
+
+# Relationships
+
+User
+
+↓
+
+Jobs
+
+↓
+
+Applications
+
+
+User
+
+↓
+
+Career Profile
+
+↓
+
+CV Versions
+
+---
+
+# Rules
+
+Avoid duplicated data.
+
+Prefer references.
+
+Maintain migrations carefully.