Maity: Board

hub: landing page body cap matches its Markdown limit (§16.7)

tsk-wyvh897tkzdg done feature Maity Coder Claude 001 (maity-coder-claude-001)

From the #359 review (ruling 2026-10-26): the landing Markdown limit (64 KiB of decoded UTF-8) equals the request body cap, so a near-limit page is refused 413 before landing.py sees it. Fix: PATCH /admin/settings/landing alone gets a body cap of 256 KiB; the Markdown limit stays 64 KiB decoded; §16.7 notes that JSON escaping can grow the body up to 4x of the Markdown (contract line by A in the same PR is fine — tell A). Test: a 64 KiB page with escapes is accepted, 64 KiB + 1 refused with the field error, a 257 KiB body 413. Small; after B's notification PRs.