Add Markdown negotiation for agents

[ashryanbeats]

Summary

• adds a build-generated English/Japanese Markdown representation of the homepage
• adds route-scoped Cloudflare Pages Functions for / and /ja/ that negotiate Accept: text/markdown
• keeps browser HTML and static assets on the existing static path
• adds _routes.json, generated-content ignore rules, and Knip entry configuration
• validates event/member-feed links and includes current event, RSVP, map, community, and published member-content links

Verification

• npm run check
• npm run build
• npx astro build
• focused negotiation/content tests
• local function simulation confirms 200, text/markdown, and Vary: Accept

Preview acceptance

The deployed preview should confirm:

curl -H 'Accept: text/markdown' -D - https://preview-url/
curl -D - https://preview-url/
curl -H 'Accept: text/markdown' -D - https://preview-url/ja/

The first and third requests should return Markdown; the browser request should remain HTML.

[cloudflare-workers-and-pages]

Deploying kyoto-tech-github-io with    Cloudflare Pages

Latest commit:	091ad18
Status:	✅  Deploy successful!
Preview URL:	https://f515e91c.kyoto-tech-github-io.pages.dev
Branch Preview URL:	https://dev-markdown-for-agents.kyoto-tech-github-io.pages.dev

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