day11/doc: replace odoc-store with compile layers + shared HTML
Replace the per-dep RO bind mount strategy for .odoc files with
regular content-addressed compile layers stacked via overlayfs.
- Compile phase: dep compile layers stacked as overlayfs lowers,
.odoc output captured in layer's fs/home/opam/odoc-out/...
- Link phase: doc-dep compile layers stacked (wider set including
{post} and x-extra-doc-deps), HTML written via RW mount to
shared os_dir/html/
- Doc-all: combines both, captures compile layer + writes HTML
This eliminates:
- Odoc_store compile_mounts/link_mounts/doc_all_mounts
- Per-dep RO bind mounts (PAGE_SIZE scaling issue)
- dep_locs hashtable tracking
- is_compiled empty-directory bug
Odoc_store stripped to just rel_path + container_html constants.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>