docs site: add MkDocs publishing layer (build, deploy, push-to-main webhook)

Renders the repository's Markdown (which stays where it is) into a
member-readable static site with Material for MkDocs: co-op brand colours
and logo, self-hosted OFL Figtree, offline search, no external hosts.

- publishing/build.sh   stage .site-src, render .site-build (mkdocs --strict)
- publishing/deploy.sh  write the build into the Surfer app container
- publishing/webhook-receiver.py + .service   Gitea push hook on main
                        triggers pull -> build -> deploy (agent host, no new
                        Cloudron app)

publishing/brand.css

@@ -0,0 +1,145 @@
+/* Inference Cooperative brand layer for the documentation site.
+ *
+ * Source of truth: the co-op's website (repos/website/index.html) — its CSS
+ * custom properties and its Figtree webfont. This file reuses those values so
+ * the documentation reads as the same organisation, not a default theme.
+ *
+ * Standing constraint: everything here is local. No third-party font service
+ * (the Google Fonts and gstatic hosts), no CDN, no other external host.
+ */
+
+:root {
+  /* -- the co-op's palette (copied from repos/website/index.html) -- */
+  --cream: #faf8f5;
+  --white: #ffffff;
+  --ink: #2d3327;
+  --muted: #6b7a62;
+  --light-muted: #94a08c;
+  --green-deep: #5b8c5a;
+  --green-mid: #6ba86b;
+  --green-light: #7ab87a;
+  --border: #e8e2d8;
+  --wash: #eef4ea;
+  --earth-red: #a04b3a;
+  --earth-red-wash: #f3e6e1;
+  --bronze: #a97a4a;
+  --bronze-wash: #f1e8da;
+}
+
+/* ---------- Material for MkDocs: map the palette onto the theme ---------- */
+
+:root,
+[data-md-color-scheme="default"] {
+  --md-default-bg-color: var(--cream);
+  --md-primary-fg-color: var(--green-deep);
+  --md-primary-fg-color--light: var(--green-mid);
+  --md-primary-fg-color--dark: #4a7a49;
+  --md-primary-bg-color: var(--cream);
+  --md-accent-fg-color: var(--earth-red);
+  --md-typeset-a-color: var(--green-deep);
+  --md-typeset-color: var(--ink);
+  --md-footer-bg-color: var(--wash);
+  --md-footer-fg-color: var(--ink);
+  --md-footer-fg-color--light: var(--muted);
+  --md-code-bg-color: #f2efe9;
+  --md-code-fg-color: var(--ink);
+  --md-admonition-bg-color: var(--wash);
+}
+
+/* Dark scheme keeps the same accents; light stays the default. */
+[data-md-color-scheme="slate"] {
+  --md-primary-fg-color: #3f6b3e;
+  --md-accent-fg-color: #d98a75;
+  --md-typeset-a-color: var(--green-light);
+  --md-code-bg-color: #2e3328;
+  --md-code-fg-color: #e8e2d8;
+}
+
+/* ---------- Typography: Figtree, self-hosted (SIL OFL 1.1) ---------- */
+
+@font-face {
+  font-family: "Figtree";
+  font-style: normal;
+  font-weight: 400;
+  font-display: swap;
+  src: url("fonts/figtree-400.woff2") format("woff2");
+}
+@font-face {
+  font-family: "Figtree";
+  font-style: normal;
+  font-weight: 500;
+  font-display: swap;
+  src: url("fonts/figtree-500.woff2") format("woff2");
+}
+@font-face {
+  font-family: "Figtree";
+  font-style: normal;
+  font-weight: 600;
+  font-display: swap;
+  src: url("fonts/figtree-600.woff2") format("woff2");
+}
+@font-face {
+  font-family: "Figtree";
+  font-style: normal;
+  font-weight: 700;
+  font-display: swap;
+  src: url("fonts/figtree-700.woff2") format("woff2");
+}
+
+:root {
+  --md-text-font-family: "Figtree", system-ui, -apple-system, "Segoe UI",
+    Roboto, "Helvetica Neue", Arial, sans-serif;
+  --md-code-font-family: ui-monospace, "SFMono-Regular", "Cascadia Mono",
+    "Segoe UI Mono", Menlo, Consolas, monospace;
+}
+
+/* ---------- Friendly details ---------- */
+
+/* Links read like the website's: brand green, semibold, underline on hover. */
+.md-typeset a {
+  font-weight: 600;
+}
+.md-typeset a:hover,
+.md-typeset a:focus {
+  text-decoration: underline;
+}
+
+/* Rounder cards and tables; a wash instead of grey where the theme has one. */
+.md-typeset .grid.cards > ul > li,
+.md-typeset .grid > .card,
+.md-typeset table:not([class]) {
+  border-radius: 0.6rem;
+}
+.md-typeset table:not([class]) {
+  border: 1px solid var(--border);
+}
+
+/* Header: co-op green with the cream wordmark. */
+.md-header {
+  box-shadow: none;
+  border-bottom: 1px solid rgba(255, 255, 255, 0.25);
+}
+.md-header .md-header__title {
+  font-weight: 600;
+}
+
+/* Tabs and the search field pick up the wash. */
+.md-tabs {
+  background-color: var(--green-deep);
+}
+.md-search__input {
+  background-color: rgba(255, 255, 255, 0.92);
+}
+
+/* Admonitions get the co-op's washes instead of stock greys. */
+.md-typeset .admonition,
+.md-typeset details {
+  border-radius: 0.6rem;
+}
+.md-typeset .admonition.tip,
+.md-typeset .admonition.note {
+  border-color: var(--green-mid);
+}
+.md-typeset .admonition.warning {
+  border-color: var(--earth-red);
+}