refactor: build dogfood image as base + mise oci layers (#25448)

Splits the dogfood image into two artifacts:

- `ghcr.io/coder/oss-dogfood-base:<distro>-<base-sha>`: Ubuntu base with
apt packages, chrome, rustup, brew, gh, and the mise binary. The
base-sha is a cache key over `Dockerfile.base` and `files/`, so commits
that don't touch those inputs reuse the previous build.
- `codercom/oss-dogfood:<final-sha>-<distro>` and rolling tags
(`:22.04`, `:26.04`, `:latest`, `:<branch>`): produced by `mise oci
build` on top of the base, with one content-addressed OCI layer per mise
tool. The rolling tag scheme is unchanged, so the workspace template
doesn't need updating.

Single-tool version bumps now invalidate only that tool's OCI layer, so
workspaces re-pull just what changed instead of the entire 5-6 GB image
on every recreate.

Also:

- Drops the build-time `pnpm dlx playwright@1.47.0 install --with-deps
chromium` step (~400 MB) and the equivalent `playwright-driver.browsers`
install from `flake.nix`. `@playwright/mcp` (used by the claude-code and
codex MCP servers in `dogfood/coder/main.tf`) does NOT auto-install
browsers, so the existing `install-deps` `coder_script` now runs two
installs on workspace start: `pnpm exec playwright install chromium` for
the site's pinned `@playwright/test`, and `npx
--package=@playwright/mcp@latest playwright-core install --no-shell
chromium` so the MCP servers find their matching browser revision.
Browser revisions coexist under
`~/.cache/ms-playwright/chromium-<rev>/`, which lives on the home volume
so both downloads happen once per workspace recreate and persist across
restarts. Net effect: same MCP behavior as before, +~1-2 min on first
workspace start. Nix devshell users running site e2e tests locally now
need `pnpm exec playwright install` once (instead of getting browsers
via nixpkgs).
- Bumps the pinned mise binary to v2026.5.12 (matching main after
#25521) and adds top-level `min_version = "2026.5.12"` to `mise.toml` so
every consumer (devs, CI, the embedded mise inside the dogfood image,
mise oci builds) fails fast on an older mise.
- Adds bison, flex, libicu-dev, libreadline-dev, uuid-dev, and
zlib1g-dev to both Ubuntu base images for source-build use cases (e.g.,
building Postgres from source).
- Replaces skopeo with crane as the registry client `mise oci push`
shells out to: crane is added to `mise.toml`, the workflow drops its
`apt-get install skopeo` and forces `--tool crane`, and the local
wrapper image stops bundling skopeo. One source of truth for tool
versions, no apt drift, smaller wrapper image, and workspace users get a
registry client on PATH for free via mise oci's tool layers.
- Removes `nix.hash`/`mise.hash` and their Makefile rules. The registry
digest already captures every effective change since CI rebuilds when
any baked-in input moves; the per-file `filesha1()` entries in
`pull_triggers` are redundant.

Supersedes #25400 (the `mise.hash` pull trigger landed there in
`2b612abe7b`; this PR removes it as part of the broader simplification).

> [!NOTE]
> `mise oci build` is experimental and requires `MISE_EXPERIMENTAL=1`
(set at job level in the workflow). The local-only
`scripts/dogfood/mise-oci-wrapper.sh` builds a tiny
`coderdev/mise-oci-wrapper:<version>` Debian image with curl-installed
mise on first invocation (cached by version tag thereafter); we don't
reuse `jdxcode/mise:latest` because that tag lags upstream GitHub
releases by days and would defeat the `min_version` enforcement above.

> [!NOTE]
> `compute-base-sha.sh` and `compute-final-sha.sh` are cache keys, not
strict content addresses: the base Dockerfile still pulls dynamic
resources at build time (gh/buildx `releases/latest`, chrome
`stable_current_amd64.deb`, apt mirror state). Two runs with identical
checked-in files can produce slightly different bytes, which is
acceptable here because the cache-hit savings on irrelevant commits
outweigh that drift.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: Thomas Kosiewski <tk@coder.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mise.toml

@@ -1,3 +1,7 @@
+# Keep in lockstep with MISE_VERSION in dogfood/coder/ubuntu-*/Dockerfile.base,
+# .github/workflows/dogfood.yaml, and scripts/dogfood/mise-oci-wrapper.sh.
+min_version = "2026.5.12"
+
 [settings]
 lockfile = true
 
@@ -28,6 +32,10 @@ protoc-gen-go = "1.30.0"
 # Infrastructure, release, and lint CLIs.
 "aqua:ahmetb/kubectx/kubens" = "0.9.4"
 cosign = "2.4.3"
+# crane is the registry client `mise oci push` shells out to. Sourced
+# here so it travels with the rest of the mise toolset (one source of
+# truth, deterministic version, no apt drift across CI / wrapper).
+crane = "0.21.6"
 golangci-lint = "1.64.8"
 helm = "3.21.0"
 kubectx = "0.9.4"
@@ -61,3 +69,16 @@ lazygit = "0.61.1"
 [tools."go:github.com/coder/sqlc/cmd/sqlc"]
 version = "337309bfb9524f38466a5090e310040fc7af0203"
 install_env = { CGO_ENABLED = "1" }
+
+# Consumed by `mise oci build` to produce the dogfood image on top of
+# ghcr.io/coder/oss-dogfood-base. The `from` and `--tag` fields are
+# overridden by CLI args at build time per distro; `mount_point`,
+# `user`, and `workdir` always apply.
+#
+# mount_point MUST match the path the base image reserves and exposes
+# via `MISE_SHARED_INSTALL_DIRS`. Both Dockerfile.base files hardcode
+# /opt/mise/data in their `install --directory`, ENV, and PATH lines.
+[oci]
+mount_point = "/opt/mise/data"
+user = "coder"
+workdir = "/home/coder"