v1.17.2: bump opencode 1.16.2->1.17.2, deprecate pi, pin+patch mempalace

opencode-ai 1.16.2 -> 1.17.2 (OPENCODE_VERSION).

Deprecate all pi support ahead of v2.0.0 removal (pi now ships from the
standalone joakimp/pi-devbox image, v1.0.0+, which no longer FROMs
base-pi-only):
- build-time stderr deprecation warning when INSTALL_PI=true
- README / DOCKER_HUB.md / AGENTS.md mark the with-pi/omos-with-pi/pi-only
  variants + base-pi-only tag deprecated, point to pi-devbox
- docs/CLEANUP-v2.0.0.md committed as the removal plan
- CHANGELOG pre-announces the v2.0.0 NPM_CONFIG_PREFIX relocation

Harden mempalace install (mirrors pi-devbox):
- pin via MEMPALACE_VERSION ARG (default 3.4.0); unpinned install is what
  swept in the broken schema
- idempotent, self-deactivating patch stripping the top-level anyOf from
  mempalace_diary_write input_schema (Anthropic tools API rejects it).
  Upstream: MemPalace/mempalace#1728, PR #1735

Fold prior Unreleased smoke-test pi-extensions readiness fix into v1.17.2.

DOCKER_HUB.md

@@ -10,15 +10,16 @@ Designed for teams who want a reproducible coding-agent setup that runs the same
 |---|---|
 | `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/earendil-works/pi) as alternative/complementary harness (shares the mempalace install with opencode) |
-| `latest-omos-with-pi` / `vX.Y.Z-omos-with-pi` | OMOS + pi together |
+| `latest-with-pi` / `vX.Y.Z-with-pi` | **DEPRECATED (removed in v2.0.0)** — Base + [pi](https://github.com/earendil-works/pi). Use [`joakimp/pi-devbox`](https://hub.docker.com/r/joakimp/pi-devbox) instead |
+| `latest-omos-with-pi` / `vX.Y.Z-omos-with-pi` | **DEPRECATED (removed in v2.0.0)** — OMOS + pi together |
 
 All variants support `linux/amd64` and `linux/arm64`.
 
-> A fifth, pi-without-opencode build is produced from the same `Dockerfile.variant`
-> (`INSTALL_OPENCODE=false`) but is **not** published under this repo — it ships as
-> the separate [`joakimp/pi-devbox`](https://hub.docker.com/r/joakimp/pi-devbox)
-> image so an "opencode-devbox" tag never lacks opencode.
+> **Looking for pi?** The `*-with-pi` / `pi-only` builds and the `base-pi-only`
+> tag are **deprecated since v1.17.2 and will be removed in v2.0.0**. pi now
+> ships as its own self-contained image:
+> [`joakimp/pi-devbox`](https://hub.docker.com/r/joakimp/pi-devbox). Pull that
+> directly instead of any pi-bearing opencode-devbox tag.
 
 ## Quick Start