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/file-security.md

@@ -0,0 +1,56 @@
+# File Security
+
+## Purpose
+
+Protect uploaded documents.
+
+---
+
+# File Types
+
+Potential uploads:
+
+- PDF.
+- DOCX.
+- Images.
+- Portfolio files.
+
+---
+
+# Validation
+
+Check:
+
+- File type.
+- File size.
+- File contents.
+
+Never trust extensions.
+
+---
+
+# Processing
+
+Uploaded files may contain:
+
+- Malicious content.
+- Embedded scripts.
+- AI prompt injection.
+
+Treat as untrusted.
+
+---
+
+# Storage
+
+Requirements:
+
+- Secure naming.
+- Access control.
+- User ownership checks.
+
+---
+
+# PDF Processing
+
+Never directly trust extracted text.