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/ai-architecture.md

@@ -0,0 +1,56 @@
+# AI Architecture
+
+## Purpose
+
+Centralise AI functionality.
+
+---
+
+# AI Service Layer
+
+Applications should not directly call AI providers.
+
+Instead:
+
+Feature
+
+↓
+
+AI Service
+
+↓
+
+Provider
+
+↓
+
+Model
+
+---
+
+# Providers
+
+Support:
+
+- OpenAI.
+- Gemini.
+- Claude.
+- Groq.
+- Ollama.
+
+---
+
+# Requirements
+
+Support:
+
+- Switching providers.
+- Usage tracking.
+- Error handling.
+- Cost control.
+
+---
+
+# Rules
+
+AI output requires validation.