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/overview.md

@@ -0,0 +1,64 @@
+# Security Overview
+
+## Purpose
+
+Define security requirements for Jobjakt.
+
+The application stores sensitive career information including:
+
+- CVs.
+- Employment history.
+- Personal details.
+- Job applications.
+- Documents.
+- Communication.
+
+Security must be considered a core product requirement.
+
+---
+
+# Security Goals
+
+Jobjakt should provide:
+
+- Secure authentication.
+- Strong user separation.
+- Safe document handling.
+- Protected APIs.
+- Secure AI integrations.
+
+---
+
+# Security Principles
+
+## Least Privilege
+
+Users should only access their own data.
+
+Admins have additional permissions.
+
+---
+
+## Secure By Default
+
+Features should default to safe behaviour.
+
+---
+
+## Validate Everything
+
+All external input should be considered untrusted.
+
+Sources:
+
+- Forms.
+- APIs.
+- Uploaded files.
+- AI responses.
+- Imported job descriptions.
+
+---
+
+## Do Not Over-Engineer
+
+Security should protect users without harming usability.