Move the canonical repo to Gitea; GitHub becomes a private archive

git.karti.ai/PIG/PIG-Demo is now the source of truth, public and anonymously
cloneable. Every self-link in the site and the docs repoints there — Gitea
serves file paths at /src/branch/main/, not /blob/main/, so those needed
rewriting rather than a hostname swap.

CI moves with it. An archived GitHub repo is read-only and its Actions stop
firing, so leaving the workflow there would have meant a repo whose gates
silently never run. .github/ is deleted rather than kept for reference: a
workflow that can never execute is worse than no workflow, because it looks
like coverage.

The Gitea workflow is not a copy. That runner is aarch64 and installs pnpm
through corepack from `packageManager` rather than pnpm/action-setup, uses
checkout@v4 and setup-node@v4, and fetches uv from astral.sh directly. It is
also configured `container.network: host` — nothing here needs a service
container, but the comment says so, because that setting cost the sibling repo
three failed runs.

The header and footer icon changed from the GitHub mark to a neutral one. A
GitHub logo pointing at a Gitea instance is a small lie about where the code
lives, on a site whose argument is that you can go and check it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019mt6sHQHEnEYrJZvoMCJSB

src/components/site/SiteHeader.tsx

@@ -1,6 +1,6 @@
 import * as React from 'react';
 import { Link } from 'react-router-dom';
-import { ArrowRight, ArrowUpRight, Github, Menu } from 'lucide-react';
+import { ArrowRight, ArrowUpRight, GitBranch, Menu } from 'lucide-react';
 
 import { listDemos } from '@/lib/demo-kit/registry';
 import type { DemoMeta } from '@/lib/demo-kit/types';
@@ -440,8 +440,8 @@ function MobileNav({
             rel="noreferrer noopener"
             className="tap flex items-center justify-between border-b border-border py-3 text-sm font-medium text-fg"
           >
-            Source on GitHub
-            <Github aria-hidden="true" className="size-4 text-muted" />
+            Source on Gitea
+            <GitBranch aria-hidden="true" className="size-4 text-muted" />
           </a>
 
           <div className="flex items-center gap-1 pt-3">
@@ -534,9 +534,9 @@ export function SiteHeader() {
                 href={REPO_URL}
                 target="_blank"
                 rel="noreferrer noopener"
-                aria-label="Source on GitHub"
+                aria-label="Source on Gitea"
               >
-                <Github aria-hidden="true" />
+                <GitBranch aria-hidden="true" />
               </a>
             </Button>
           </div>