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/model-selection.md

@@ -0,0 +1,60 @@
+# AI Model Selection
+
+## Goal
+
+Use appropriate models for tasks.
+
+---
+
+# Task Categories
+
+## Simple Tasks
+
+Examples:
+
+- Grammar correction.
+- Shortening text.
+
+Use:
+
+Fast/cheap models.
+
+---
+
+## Complex Tasks
+
+Examples:
+
+- CV generation.
+- Career analysis.
+
+Use:
+
+Higher quality models.
+
+---
+
+## Long Context Tasks
+
+Examples:
+
+- Analysing full CV.
+- Comparing job descriptions.
+
+Use:
+
+Large context models.
+
+---
+
+# Principles
+
+Do not use expensive models unnecessarily.
+
+Balance:
+
+Quality.
+
+Speed.
+
+Cost.