docs: add industry use cases and WikiLoop in industry pages

[jasen215]

Summary

Add two new pages to the Ecosystem section (EN + ZH):

1. WikiLoop in Industry (ecosystem/wikiloop-industries.md)

• Covers 8 industries: law firms, accounting, healthcare, financial services, manufacturing, government/defense, energy/nuclear, research institutions
• Each industry: privacy concern → specific use cases → deployment approach
• Standalone sections: private deployment architecture diagram, cloud RAG vs WikiLoop comparison table (8 dimensions)
• Highlights air-gap, zero-infrastructure, local LLM, OKF portability, git auditability advantages

2. Industry Use Cases (ecosystem/use-cases.md)

• 10 main industries + 5 additional industries
• Each industry: KB contents, use case table (who/how), RAG vs LLM Wiki recommendation
• WikiLoop fit table across industries
• Selection decision framework

Navigation: New top-level "WikiLoop" group in Ecosystem sidebar, WikiLoop pages placed first.

Test plan

• Local pnpm docs:build passes
• Confirm https://jasen215.github.io/wikiloop/ecosystem/wikiloop-industries accessible after merge
• Confirm https://jasen215.github.io/wikiloop/ecosystem/use-cases accessible after merge