docs: fix stale variant/job counts missed in pi-only sweep

- AGENTS.md: 'eight load:true jobs' -> ten (add validate-pi-only, smoke-pi-only)
- .gitea/README.md: 'four variants / eight tags' -> five / ten
- docs/manual-host-publish.md: 'Variants x4 / 10 tags' -> x5 / 12 tags

These are living operational facts; the remaining 'four/eight' hits are
illustrative meta-instructions or dated historical CHANGELOG entries (correct
as-is).

AGENTS.md

@@ -99,7 +99,7 @@ cd /tmp && npm pack @earendil-works/pi-coding-agent@0.75.5 && tar -xzf earendil-
 - `update-description` job runs only when both builds succeed (`needs: [build-base, build-omos]`).
 - Tags must be pushed to trigger the publish workflow. The validate workflow runs on push to main and PRs.
 - Smoke tests run on amd64 only (single-arch load into the local daemon). The multi-arch push happens after smoke passes.
-- **Gitea Actions runner has ~40 GB disk, often 70%+ used at job start.** All eight `load: true` jobs (`validate-base`, `validate-omos`, `validate-with-pi`, `validate-omos-with-pi`, `smoke-base`, `smoke-omos`, `smoke-with-pi`, `smoke-omos-with-pi`) include a `Reclaim runner disk` step that strips catthehacker-resident toolchains and prunes stale docker state before `setup-buildx-action`. Build jobs use a lighter version (push-by-digest doesn't need `docker system prune`). Don't remove these steps without testing on a fresh runner.
+- **Gitea Actions runner has ~40 GB disk, often 70%+ used at job start.** All ten `load: true` jobs (`validate-base`, `validate-omos`, `validate-with-pi`, `validate-omos-with-pi`, `validate-pi-only`, `smoke-base`, `smoke-omos`, `smoke-with-pi`, `smoke-omos-with-pi`, `smoke-pi-only`) include a `Reclaim runner disk` step that strips catthehacker-resident toolchains and prunes stale docker state before `setup-buildx-action`. Build jobs use a lighter version (push-by-digest doesn't need `docker system prune`). Don't remove these steps without testing on a fresh runner.
 - **`docker/build-push-action@v7` with `platforms: linux/amd64,linux/arm64` handles multi-arch push natively in a single job** — produces a proper manifest list, no matrix or merge step needed. An earlier revision split into per-arch matrix jobs with digest artifacts, but that pattern requires `actions/{upload,download}-artifact@v4+` which Gitea Actions doesn't support (see below).
 - **`actions/upload-artifact` and `actions/download-artifact` must stay at @v3 on Gitea.** v4+ uses a GitHub-Enterprise-specific Artifact API; runs fail with `GHESNotSupportedError`. If you need artifacts for a new reason (build logs, SBOMs, etc.), pin @v3 explicitly.
 - **Step scripts run under `/bin/sh` (dash), not bash.** Avoid bash-isms like `${VAR//a/b}` parameter-pattern substitution; use POSIX alternatives (`tr`, `sed`) or declare `shell: bash` on the step.