docs: remove obsolete Codex workflow documentation

Removed 7 Codex-specific workflow files:
- CODEX-QUICK-START-PROMPT.md
- CODEX-STRATEGIC-WORKFLOW-TEMPLATE.md
- codex-strategic-analyses.md
- codex-workflow.md
- cove-72h-workflow.md
- dspy-model-export-workflow.md
- dspy-optimization-workflow.md

Reason: Codex CLI usage has evolved; these templates no longer reflect
current workflow patterns. Agent system (15 operational agents) now
primary orchestration mechanism.

Reference: workspace/docs/Obsidian-v2/docs/reference/tools/codex-cli.md
for current Codex usage patterns.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Michael