feat: El-native landing replaces the Next.js site, Dockerfile + build.sh

Hand-cuts the marketing surface from Next.js to a native El HTTP server.
The El landing reads the pre-rendered index.html (output of the existing
component pipeline at src/index.html) and serves it directly. ~150
lines of El at server.el; 130 KB binary; no Node, no build step at
serve-time, no runtime JS for the marketing pages.

What's here:

  - server.el: dispatcher with /, /health, /api/founding-count, /assets/*,
    /brand/*, 404 JSON for everything else. Routes go through fs_read
    against LANDING_ROOT (default /srv/landing in the container, ./src
    locally).

  - Dockerfile: two-stage build for linux/amd64 (Cloud Run target).
    Stage 1 — debian:bookworm-slim with build-essential + libcurl-dev,
    compiles the binary against el_runtime.c. Stage 2 — slim runtime
    image with libcurl4 + ca-certificates, drops the binary at
    /usr/local/bin/landing, copies src/index.html and src/assets/ into
    /srv/landing/. Uses -rdynamic so the runtime's dlsym(RTLD_DEFAULT,
    handler_name) can find handle_request inside the executable on
    glibc — macOS exposes executable symbols by default, Linux does
    not. Links -lcurl -lpthread -ldl -lm; the C feature-test macros
    (_GNU_SOURCE) are now in el_runtime.c itself.

  - build.sh: stages the foundation El runtime into ./runtime/, runs
    elc to regenerate server.c, builds the docker image. --tag and
    --push flags. Push targets us-central1-docker.pkg.dev/neuron-785695/
    neuron-marketing/marketing for the Cloud Run flip (still manual).

  - .gitignore: runtime/, /server.c, build/ — all build artifacts.

The path here was non-trivial. The original goal was to compile the
full 4325-line landing-combined.el end-to-end; that OOM'd at 8.7 GB
under the always-allocate-fresh el_list_append (the workaround for an
aliasing bug in cg_if_stmt). The runtime ARC scaffolding committed
earlier today got the compile down to 3.5 GB peak in 0.26s, but the
landing-combined still has pre-existing source bugs (http_serve(3001)
arity, neuron_origin bare expression statement) that block the build.
The structurally cleaner path was to render the HTML once, offline, and
serve the static output — which is what this server.el does. The
landing-combined.el can be revisited when those source bugs are fixed;
this server.el is the canonical production surface in the meantime.

Did not commit ./runtime/ (gitignored, staged from foundation by
build.sh on each build), ./server.c (generated by elc from server.el),
or ./build/ (build artifacts). The repo carries the source of truth
only.

build.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+#
+# build.sh — Build the El landing Docker image.
+#
+# Pipeline:
+#   1. Stage the foundation El runtime into ./runtime/ (Docker needs it
+#      inside the build context — symlinks don't cross context boundaries
+#      cleanly on every Docker version).
+#   2. Compile server.el to server.c using the canonical elc at
+#      foundation/el/dist/platform/elc.
+#   3. docker buildx build for linux/amd64 (Cloud Run runs amd64 images).
+#
+# Both the staged ./runtime/ and the generated ./server.c are git-ignored
+# — they're build artifacts. server.el and the Dockerfile are the source
+# of truth.
+#
+# Usage:
+#   ./build.sh           — build neuron-landing:dev locally
+#   ./build.sh --tag X   — build with a specific tag
+#   ./build.sh --push    — also push to GCP Artifact Registry (won't
+#                          activate; Cloud Run service flip is manual)
+
+set -euo pipefail
+
+cd "$(dirname "$0")"
+
+LANDING_DIR=$(pwd)
+EL_HOME="${EL_HOME:-${LANDING_DIR}/../../../foundation/el}"
+ELC="${EL_HOME}/dist/platform/elc"
+RUNTIME_SRC="${EL_HOME}/el-compiler/runtime"
+
+TAG="dev"
+PUSH=0
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --tag) TAG="$2"; shift 2 ;;
+        --push) PUSH=1; shift ;;
+        *) echo "unknown flag: $1" >&2; exit 1 ;;
+    esac
+done
+
+echo "==> Staging El runtime from ${RUNTIME_SRC}"
+mkdir -p runtime
+cp "${RUNTIME_SRC}/el_runtime.c" runtime/
+cp "${RUNTIME_SRC}/el_runtime.h" runtime/
+
+echo "==> Compiling server.el → server.c via ${ELC}"
+"${ELC}" server.el > server.c
+
+echo "==> Building Docker image neuron-landing:${TAG} for linux/amd64"
+docker buildx build --platform linux/amd64 --load -t "neuron-landing:${TAG}" .
+
+if [ "${PUSH}" = "1" ]; then
+    REGISTRY="us-central1-docker.pkg.dev/neuron-785695/neuron-marketing"
+    REMOTE_TAG="${REGISTRY}/marketing:${TAG}"
+    echo "==> Tagging and pushing ${REMOTE_TAG}"
+    docker tag "neuron-landing:${TAG}" "${REMOTE_TAG}"
+    docker push "${REMOTE_TAG}"
+    echo "(image pushed; Cloud Run service flip is a separate step)"
+fi
+
+echo "==> Done. Run with:"
+echo "    docker run --rm -p 8080:8080 neuron-landing:${TAG}"