docs(workflow): 明确执行模式推荐与文档清理

[iamsyc]

Summary

• clarify when execution mode recommendations should be re-evaluated during analysis-to-implementation transitions
• tighten the boundary between explicit mode selection and short confirmations
• remove obsolete workflow review and optimization documents

Why

• keep agent workflow guidance aligned with current repository rules
• reduce ambiguity around when the agent should switch from analysis to execution framing
• clean up stale documents that no longer reflect the maintained process

Verification

• git diff --check main...codex/fix-execution-mode-guidance

[github-actions]

CI Summary

Run: Open

Check	Status	Details
Change Scope	non_code	non-code pull request fast-path
Unit Tests	skipped	skipped; non-code pull request
UI Smoke Tests (matrix: baseline + permissionDenied + rebuildFailed)	skipped	skipped; non-code pull request
Release Build Check (Release arch smoke: arm64 + x86_64)	skipped	skipped; non-code pull request
CI Gate	success	required; non-code PR fast-path

Gate rule: 本次 PR 仅包含非代码变更，已跳过 Unit Tests / UI Smoke Tests / Release Build Check，ci-gate 直接通过。