feat(runner): install the build toolchain compiled languages need

The runner is host-mode, so there is no image bringing tools along: what is
not on this LXC, no job has. Measured on l.kirchner/patchmgr, a Go project,
where all six CI jobs were assigned and every one of them died in the first
seconds:

    make all         make: command not found
    go test -race    go: -race requires cgo; enable cgo by setting CGO_ENABLED=1
    make proto       sudo: command not found

Four packages, each for a reason:

    make               the gate commands are make targets
    gcc                Go turns CGO_ENABLED off when it finds no C compiler,
                       and the race detector cannot be built without cgo
    protobuf-compiler  protoc itself
    libprotobuf-dev    the well-known .proto includes under
                       /usr/include/google/protobuf; without them protoc fails
                       even though the binary is there

sudo stays absent on purpose. A workflow must not be able to install anything
on this runner -- what is needed is declared here, in the script, and not in
somebody's pipeline. That also keeps the security note at the top of this file
honest: the LXC owns nothing, and it gains nothing at a workflow's request.

Go is not in the list. Projects fetch it through actions/setup-go, because CI
matrices run more than one version.

Applied to the running LXC (301 on pve-gamer) while the runner was idle, then
verified: make 4.3, gcc 12.2.0, libprotoc 3.21.12, 11 .proto includes present.
The service PATH already contains /usr/bin, so no restart was needed.

install/runner-install.sh

@@ -63,8 +63,26 @@ valid_token_word "$RUNNER_LABELS" || { msg_err "RUNNER_LABELS enthält unzuläss
 # der unprivilegierte User darf dort nicht schreiben.
 run_user() { runuser -u "$APP_USER" -- env -C "$RUNNER_DIR" HOME="$APP_HOME" "$@"; }
 
-# ── Pakete: git/rsync, Node (checkout-Action), Docker (Test-Container) ────────
-setup_base_apt git rsync ca-certificates curl
+# ── Pakete: git/rsync, Node (checkout-Action), Docker (Test-Container),
+#    Build-Werkzeuge (Compiler-Sprachen in CI) ─────────────────────────────────
+#
+# make/gcc/protobuf: Der Runner faehrt Host-Mode, also gibt es kein Image, das
+# Werkzeuge mitbringt — was hier nicht liegt, hat kein Job. Konkret gemessen an
+# l.kirchner/patchmgr (Go):
+#   make                 "make: command not found" in jedem Gate-Job
+#   gcc                  ohne C-Compiler setzt Go CGO_ENABLED=0, und
+#                        "go test -race" ist dann gar nicht baubar
+#   protobuf-compiler    protoc fuer die Codegenerierung
+#   libprotobuf-dev      liefert /usr/include/google/protobuf/*.proto; ohne die
+#                        Includes scheitert protoc trotz vorhandenem Binary
+#
+# Bewusst NICHT installiert: sudo. Ein Workflow soll auf diesem Runner nichts
+# nachinstallieren koennen — was gebraucht wird, steht hier.
+#
+# Go selbst gehoert nicht hierher: Projekte holen es ueber actions/setup-go,
+# weil CI-Matrizen mehrere Fassungen fahren.
+setup_base_apt git rsync ca-certificates curl \
+  make gcc protobuf-compiler libprotobuf-dev
 
 NODE_HAVE="$(command -v node >/dev/null 2>&1 && node -v | sed -E 's/^v([0-9]+).*/\1/' || echo 0)"
 if [[ "$NODE_HAVE" != "$NODE_MAJOR" ]]; then