docs: surface with-pi and omos-with-pi variants on Docker Hub

The v1.14.41b release expanded the CI matrix to four image variants
and pushed eight tags total, but the docs lagged behind:

- DOCKER_HUB.md's Image Variants table still listed only base + omos.
- README.md's pi section only described building from source; no
  mention that prebuilt latest-with-pi / latest-omos-with-pi tags
  exist (asymmetric vs the OMOS section which does mention latest-omos).

Fix:
- generate-dockerhub-md.py HEADER: extend Image Variants table to all
  four variants (base, omos, with-pi, omos-with-pi).
- README.md pi section: add a Setup subsection mentioning the prebuilt
  pi-enabled tags, mirroring the OMOS section's pattern.
- Regenerate DOCKER_HUB.md (22975 bytes, well under the 25k Hub limit).

The pi section itself remains intentionally dropped from DOCKER_HUB.md
to fit the 25k limit (SECTION_RULES); the Image Variants table at the
top is sufficient signal for Hub readers.

DOCKER_HUB.md

@@ -4,14 +4,16 @@ Portable AI developer environment for [opencode](https://opencode.ai). Debian-ba
 
 ## Image Variants
 
-Two image variants are published for each release:
+Four image variants are published for each release:
 
 | Tag | Description |
 |---|---|
 | `latest` / `vX.Y.Z` | Base image — opencode, Node.js, AWS CLI, dev tools |
 | `latest-omos` / `vX.Y.Z-omos` | Base + [oh-my-opencode-slim](https://github.com/alvinunreal/oh-my-opencode-slim) multi-agent orchestration and Bun |
+| `latest-with-pi` / `vX.Y.Z-with-pi` | Base + [pi](https://github.com/mariozechner/pi-coding-agent) as alternative/complementary harness (shares the mempalace install with opencode) |
+| `latest-omos-with-pi` / `vX.Y.Z-omos-with-pi` | OMOS + pi together |
 
-Both variants support `linux/amd64` and `linux/arm64`.
+All variants support `linux/amd64` and `linux/arm64`.
 
 > **NOTE:** This file is auto-generated from `README.md` by `scripts/generate-dockerhub-md.py`. Edit README.md and regenerate rather than editing this file directly.