release: v1.1.6 — build provenance + reproducibility hardening; pi 0.79.7 → 0.79.8

Adds OCI labels + /etc/pi-devbox/build-manifest.json so a published tag is
self-describing and reconstructable after CI logs rotate (manifest is
written from the actual checked-out HEAD of each /opt clone + live
pi --version, not just the intended build-args).

Hardens the build plumbing:
- scripts/check-base-hash.sh guards the base-rebuild invariant: every
  floating ARG *_REF in Dockerfile.base must be folded into the base_tag
  hash, else a ref-only change silently fails to rebuild the base
  (v1.1.2-class staleness footgun). Runs in base-decide and locally.
- resolve-versions now fails loud instead of falling back to a floating
  main/master on a transient API failure — validates each ref is a 40-hex
  SHA (and pi a real semver) and aborts the release otherwise.
- The three gitea companions (pi-toolkit, pi-extensions, mempalace-toolkit)
  gained overridable *_REPO build-args (defaulting to the canonical gitea
  origin) so a relocated/forked build can repoint them without editing the
  Dockerfiles — matching the existing PI_FORK_REPO/PI_OBSMEM_REPO pattern.

README documents the forked/relocated build-arg trick and how to read the
labels + manifest. smoke-test asserts the manifest + labels. pi bumps
0.79.7 → 0.79.8 (auto-resolved at build).

Dockerfile.base

@@ -351,6 +351,11 @@ RUN if [ "${INSTALL_MEMPALACE}" = "true" ]; then \
 # ── mempalace-toolkit — bash wrappers for session/docs mining ────────
 ARG INSTALL_MEMPALACE_TOOLKIT=true
 ARG MEMPALACE_TOOLKIT_REF=main
+# MEMPALACE_TOOLKIT_REPO defaults to the canonical gitea origin but is
+# overridable so a relocated/forked build can clone from a mirror or a
+# different host without editing this Dockerfile (mirrors the
+# PI_FORK_REPO / PI_OBSMEM_REPO / PI_STUDIO_REPO pattern in the variant).
+ARG MEMPALACE_TOOLKIT_REPO=https://gitea.jordbo.se/joakimp/mempalace-toolkit.git
 # MEMPALACE_TOOLKIT_REF accepts EITHER a branch name OR a commit SHA. CI
 # resolves it to a SHA (resolve-versions job) and folds that SHA into the
 # base-decide hash so the base rebuilds when the toolkit moves. `git clone
@@ -360,7 +365,7 @@ ARG MEMPALACE_TOOLKIT_REF=main
 RUN if [ "${INSTALL_MEMPALACE}" = "true" ] && [ "${INSTALL_MEMPALACE_TOOLKIT}" = "true" ]; then \
       rm -rf /opt/mempalace-toolkit && mkdir -p /opt/mempalace-toolkit && \
       git -C /opt/mempalace-toolkit init -q && \
-      git -C /opt/mempalace-toolkit remote add origin https://gitea.jordbo.se/joakimp/mempalace-toolkit.git && \
+      git -C /opt/mempalace-toolkit remote add origin "${MEMPALACE_TOOLKIT_REPO}" && \
       ok=0; for i in 1 2 3 4 5; do \
         if git -C /opt/mempalace-toolkit fetch --depth 1 origin "${MEMPALACE_TOOLKIT_REF}" && \
            git -C /opt/mempalace-toolkit checkout -q FETCH_HEAD; then ok=1; break; fi; \