A repository's home draws its README's first 64 KB and links to the rest: grokbot/forge's home under 150 KB #6201

Measured 2026-10-26: /grokbot/forge sends 351 KB because the home renders the whole 209 KB README.md (readme;dur=13). Every visitor to a fork of the forge downloads the full manual.

Done when:

• [ ] The repository home renders the README up to 64 KB of source, cut at a heading or paragraph boundary, then a link reading "Read the whole README" to its blob page.
• [ ] A README under the limit renders exactly as today.
• [ ] A test with a 200 KB README asserts the home has the link and a body under 150 KB, and that a 2 KB README has no link.

Files: the repository home's README section in src/web/pages/, a test. Risk: cutting inside a fenced code block breaks the rendering. Cut only between top-level blocks.