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/ai/cover-letter-ai.md

@@ -0,0 +1,49 @@
+# Cover Letter AI
+
+## Purpose
+
+Generate personalised cover letters.
+
+---
+
+# Inputs
+
+Use:
+
+- Career Profile.
+- Master CV.
+- Job description.
+
+---
+
+# Features
+
+Generate:
+
+- First draft.
+- Improvements.
+- Tone changes.
+
+---
+
+# User Control
+
+Allow:
+
+- Editing.
+- Regeneration.
+- Manual writing.
+
+---
+
+# Rules
+
+Avoid generic letters.
+
+Focus on:
+
+Why this person.
+
+Why this company.
+
+Why this role.