docs(flags): Document local eval with Java SDK

[dustinbyrne]

Changes

This change documents the usage of local evaluation with the server-side Java SDK. It also cleans up a few spots where Java SDK information was missing or incorrect.

• https://posthog-hxo8utpj7-post-hog.vercel.app/docs/feature-flags/local-evaluation (new)
• https://posthog-hxo8utpj7-post-hog.vercel.app/docs/libraries/java#local-evaluation (new)
• https://posthog-hxo8utpj7-post-hog.vercel.app/docs/feature-flags/installation (previously Java wasn't included on this page)
• https://posthog-hxo8utpj7-post-hog.vercel.app/docs/feature-flags/installation?tab=Java (added reference to Spring sample project, debug mode)
• https://posthog-hxo8utpj7-post-hog.vercel.app/docs/feature-flags/adding-feature-flag-code?tab=Java (new)

Checklist

• Words are spelled using American English
• Titles are in sentence case
• Feature names are in sentence case too. It's "product analytics" not "Product Analytics" and so on.
• Use relative URLs for internal links
• If I moved a page, I added a redirect in vercel.json
• Remove this template if you're not going to fill it out!

[vercel]

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Project	Deployment	Preview	Updated (UTC)
posthog	Ready	Preview	Dec 4, 2025 8:39pm

[greptile-apps]

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[haacked]

LGTM! 🚢