docs: clarify lsp configuration

[russeell]

Issue for this PR

Closes #30954

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Clarifies the difference between enabling LSP server integration with the lsp config and enabling the separate experimental lsp tool.

The tools page now says experimental tools can require feature flags, and the LSP page notes that "lsp": true enables server integration and diagnostics, not the experimental tool.

How did you verify your code works?

Docs-only change. Verified locally with:

• git diff --check
• source review of the affected docs pages and the runtime flag reference:
• packages/web/src/content/docs/tools.mdx
• packages/web/src/content/docs/lsp.mdx
• packages/opencode/src/effect/runtime-flags.ts

Docs build was not run because this local environment does not have Bun installed.

Screenshots / recordings

N/A, docs-only change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR