Keep llms-full.txt to the written pages #576

Summary

/llms-full.txt is too large for an agent to read in one request. Limit it to the written pages and point to the rest.

Context

At docs commit aeb5162, /llms-full.txt is 754,448 bytes and 91,555 words (my estimate: roughly 120,000 to 190,000 tokens). It holds all 196 pages. 127 of them are generated API operation pages under /api-reference/, and one is the 11,854-word changelog. Every page, including each operation, already has its own .md address and an entry in llms.txt.

Acceptance criteria

• /llms-full.txt holds the written pages and leaves out the generated API operation pages and the changelog.
• /llms.txt says what llms-full.txt holds and where the operations (/api-reference pages, openapi.json) and the changelog are.
• The content lint still passes, and no link in llms.txt is broken.

Out of scope

• Splitting the file into several files (decide in the pull request if one file is still too large).

Notes

src/AGENTS.md says source.config.ts decides what each component becomes in the Markdown copy. The generator for llms-full.txt is in src/routes/llms-full[.]txt.ts.