route runner build container clones via public URL with CF Access

The Gitea Actions runners on Legion need build containers to be able
to clone repos. They run with network: host so they can't resolve
gitea.git.svc.cluster.local — they have to use the public URL. The
public URL sits behind Cloudflare Access, which is why the previous
naive switch (#3) had to be reverted.

This change keeps the runner daemon registered against the in-cluster
URL (no CF Access on the polling loop) but rewrites
http://gitea.git.svc.cluster.local:3000/ to
https://git.neuralplatform.ai/ inside the build container, with the
CF Access service-token headers injected via git extraHeader.

The redirect script is sourced before every job step via BASH_ENV;
the CF Access credentials reach the build container through
act_runner's container.env, which we now populate from the new
gitea-runner-cf-access Vault path that PR #5's Terraform writes.

Known limitation documented in the init script: actions/checkout's
per-job auth header is keyed to the in-cluster URL and gets dropped
after the insteadOf rewrite. Public repos work; private repos that
need that token will need a follow-up.

servers/legion/k8s/gitea-runner/git-cf-access-init.sh

@@ -0,0 +1,50 @@
+#!/bin/sh
+# git-cf-access-init.sh
+#
+# Configures git so any clone/fetch from Gitea ends up going to
+# git.neuralplatform.ai with the runner's Cloudflare Access service-token
+# headers attached.
+#
+# How this gets invoked:
+#   The forgejo-runner job execution path runs each step via a
+#   non-interactive bash invocation inside the build container. Setting
+#   BASH_ENV=/usr/local/bin/git-cf-access-init.sh in act_runner's
+#   container.env causes bash to source this script before any step's
+#   commands run. (See servers/legion/k8s/gitea-runner/deployment.yaml.)
+#
+# What it does:
+#   1. Rewrites http://gitea.git.svc.cluster.local:3000/ → https://git.neuralplatform.ai/
+#      via insteadOf. The runner registered against the in-cluster URL (no
+#      CF Access on the daemon's polling loop), so act_runner advertises
+#      that URL to the build container as github.server_url. Build
+#      containers run with network: host and can't resolve
+#      *.svc.cluster.local, so we need to redirect to the public URL.
+#   2. Adds the CF Access service-token headers to outbound requests to
+#      git.neuralplatform.ai so the clone authenticates through CF Access.
+#
+# Idempotent — re-runs replace any prior config keys without accumulating
+# duplicate header entries.
+#
+# Known limitation: actions/checkout sets an Authorization extraheader
+# keyed to the server URL it was given (the in-cluster URL). After
+# insteadOf substitution the request goes to the public URL where git
+# matches http.<public>.extraheader, and the in-cluster-keyed
+# Authorization header is dropped. For public repos this is fine. For
+# private repos the per-job token will not be sent — see the PR
+# description for the follow-up plan if dharma-el's CI needs that token.
+
+if [ -n "${CF_ACCESS_CLIENT_ID:-}" ] && [ -n "${CF_ACCESS_CLIENT_SECRET:-}" ]; then
+    git config --global --replace-all \
+        url."https://git.neuralplatform.ai/".insteadOf \
+        "http://gitea.git.svc.cluster.local:3000/" 2>/dev/null || true
+
+    # Reset extraHeader on the public URL, then add both CF Access headers.
+    git config --global --unset-all \
+        http."https://git.neuralplatform.ai/".extraHeader 2>/dev/null || true
+    git config --global --add \
+        http."https://git.neuralplatform.ai/".extraHeader \
+        "CF-Access-Client-Id: ${CF_ACCESS_CLIENT_ID}" 2>/dev/null || true
+    git config --global --add \
+        http."https://git.neuralplatform.ai/".extraHeader \
+        "CF-Access-Client-Secret: ${CF_ACCESS_CLIENT_SECRET}" 2>/dev/null || true
+fi