Add scenario-based documentation with decision flowchart

首先检查现有的文档结构和导航，以确定场景指南和 landing pages 应放置的位置。围绕列出的 source-of-truth、branching、environment、CI/CD 和 change-flow 选项，定义 Mermaid 决策流程图。完成标准是：流程图已嵌入并得到维护，至少三个场景页面涵盖所需指南，并且文档索引链接到这些页面。

Summary

Create scenario-level documentation that guides users through key decisions (branching strategy, source of truth, environment topology, etc.) via a decision flowchart, landing them in the appropriate "how-to" doc for their chosen setup.

Problem

Users come to APIOps CLI with different organizational constraints and preferences. Currently, they must read through all documentation to figure out which setup applies to them. A guided decision tree would dramatically reduce time-to-value.

Proposed Content

Decision Flowchart

A visual flowchart (mermaid diagram or similar) that walks users through key decisions:

1. Source of Truth — Is APIM the source of truth, or is the Git repo?
2. Branching Strategy — Trunk-based, GitFlow, environment branches, etc.
3. Environment Topology — One APIM instance per environment, or multiple environments on a single instance?
4. CI/CD Platform — GitHub Actions or Azure DevOps?
5. Change Flow — Portal-first (extract → commit → promote) or code-first (edit → PR → publish)?

Scenario Landing Pages

Each leaf of the decision tree links to a dedicated "how-to" page covering:

• Recommended repo structure
• Configuration file setup (filters, overrides)
• CI/CD pipeline configuration
• Step-by-step walkthrough for the chosen scenario
• Common pitfalls and FAQ

Example Scenarios

• Scenario A: Git as source of truth, trunk-based development, separate APIM per environment, GitHub Actions
• Scenario B: Portal-first, feature branches, single APIM instance, Azure DevOps
• Scenario C: Hybrid (portal for discovery, Git for promotion), environment branches

Acceptance Criteria

• Decision flowchart is created and embedded in documentation
• At least 3 scenario landing pages are written
• Each scenario page includes repo structure, config setup, and CI/CD guidance
• Flowchart is maintained as a mermaid diagram (or similar) for easy updates
• Documentation index/nav links to the scenario guide prominently