tpm-enrol: pivot host enrolment to a Go binary, built out-of-VM

Replaces the shell/openssl-provider host enrolment (a35f2d6) with a static
Go + go-tpm binary, and moves BOTH host Go binaries out of the Packer VM.

fleet-enrol (files/enrol/, Go + go-tpm, no CGO):
  - talks to /dev/tpmrm0 DIRECTLY via transport.FromReadWriter(os.File) — no
    linuxtpm, so go-tpm is the only dep and there is NO tpm2-tools key-gen /
    openssl tpm2 provider / curl in the image (removes the biggest bench risk,
    the provider handle: key-ref).
  - ensures the ECDSA key @0x81010001, builds the CSR (crypto.Signer over the
    TPM key), POSTs CSR+context to the broker, shows the Plymouth fingerprint,
    polls /status, writes the leaf cert to NV 0x01800001.
  - tpmkey/ is an exported package so the TPM ceremony is tested against the
    go-tpm software simulator from a SEPARATE simtest/ module (CGO stays out of
    the shipped build). Transaction logic (mock broker) tested in-package.
  - deps pinned by go.sum (not vendored): the binary now builds on the CI
    runner, which has network — reproducible via pinned Go 1.26.4 + go.sum.

Out-of-VM build (decision): both fleet-enrol AND fleet-hostapi compile in the
CI "Build host Go binaries" step (Go 1.26.4, CGO off, -trimpath) and Packer
FILE-PROVISIONS the static binaries in. Dropped the in-VM `dnf install golang`
+ the 2d removal — the Rocky build image carries no Go toolchain / go-tpm tree.

Wiring:
  - tpm-enrol.sh: now a thin GATE (empty-NV check, pre-auth DHCP on en*,
    exec /usr/sbin/fleet-enrol, reboot-to-converge). module-setup.sh bundles the
    binary (asserted) + reverts the tpm2-openssl/curl installs.
  - diskless.pkr.hcl: file provisioners for both binaries; enrol installed to
    /usr/sbin before the initramfs build + fapolicyd-trusted; lsinitrd asserts
    fleet-enrol; dnf reverted to baseline (no tpm2-openssl/curl).
  - gitea-main-ci.yaml: Set up Go + build both binaries + run the simulator
    ceremony test, before packer validate.

TESTED here: transaction unit tests + the full TPM ceremony (key-gen -> persist
-> ECDSA sign -> CSR verify -> chunked NV write -> re-enrol) against the go-tpm
simulator. BENCH-VERIFY (real/swtpm, empty owner auth, pre-auth DHCP, Plymouth,
reboot-converge, prod HTTPS) tracked in docs/TODO.md #11.

.gitea/workflows/gitea-main-ci.yaml

@@ -189,6 +189,38 @@ jobs:
           # depend on the runner's shellcheck finding that rc file.
           shellcheck --exclude=SC1091,SC2154 files/dracut/95dot1x-macsec/*.sh scripts/*.sh
 
+      -
+        name: Set up Go
+        uses: actions/setup-go@v5
+        with:
+          go-version: '1.26.4'
+
+      -
+        name: Build host Go binaries out-of-VM (fleet-enrol, fleet-hostapi)
+        # Built HERE on the runner, NOT inside the Packer VM, so the Rocky build
+        # image never carries the Go toolchain or the go-tpm dep tree. Packer
+        # file-provisions the resulting static binaries into the rootfs. Runs
+        # BEFORE packer validate/build so the file provisioners' sources exist.
+        # Reproducible: pinned Go (1.26.4) + go.sum-pinned deps + -trimpath/no buildid.
+        # fleet-enrol fetches go-tpm from the proxy (pinned by go.sum); hostapi is
+        # stdlib-only (GOPROXY=off).
+        run: |
+          set -euo pipefail
+          ( cd files/enrol \
+            && CGO_ENABLED=0 GOTOOLCHAIN=local \
+               go build -trimpath -buildvcs=false -ldflags '-s -w -buildid=' -o bin/fleet-enrol . \
+            && CGO_ENABLED=0 go test ./... )
+          ( cd files/hostapi \
+            && CGO_ENABLED=0 GOPROXY=off GOTOOLCHAIN=local \
+               go build -trimpath -buildvcs=false -ldflags '-s -w -buildid=' -o bin/fleet-hostapi . )
+          file files/enrol/bin/fleet-enrol files/hostapi/bin/fleet-hostapi
+
+      -
+        name: TPM enrolment ceremony test (go-tpm software simulator)
+        # Exercises the real key-gen/sign/NV path against a software TPM (CGO in a
+        # separate module, so the simulator never enters the shipped enrol build).
+        run: ( cd files/enrol/simtest && CGO_ENABLED=1 go test ./... )
+
       -
         name: packer init
         run: packer init .