feat: add prerelease RPM builds from upstream main branch

Poll upstream main branch HEAD alongside release tags. When a new commit
is detected, build and publish prerelease RPMs to a separate unstable
repo at rpm.lair.cafe/fedora/$releasever/$basearch/unstable/.

RPM versioning uses the Fedora snapshot convention (e.g.
0.8.1-0.1.20260511git1a2b3c4.fc43) so stable releases automatically
supersede any installed prerelease.

- RPM spec: conditional Release field via mistralrs_prerelease define
- poll-upstream.yml: new check-prerelease job fetches main HEAD + Cargo.toml version
- build-prerelease.yml: new workflow for commit-based builds without --locked
- UI: fetch both stable/unstable manifests, show channel badges, add
  unstable repo setup instructions to home page

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/PackageDetail.tsx

@@ -11,13 +11,13 @@ function formatBytes(bytes: number): string {
 
 export function PackageDetail() {
   const { name } = useParams<{ name: string }>();
-  const { manifest, loading, error } = usePackages();
+  const { packages, loading, error } = usePackages();
 
   if (loading) return <Spinner animation="border" />;
   if (error) return <Alert variant="danger">Failed to load packages: {error}</Alert>;
-  if (!manifest) return <Alert variant="info">No package data available.</Alert>;
+  if (packages.length === 0) return <Alert variant="info">No package data available.</Alert>;
 
-  const versions = manifest.packages
+  const versions = packages
     .filter((p) => p.name === name)
     .sort((a, b) => b.buildTime - a.buildTime);
 
@@ -25,6 +25,7 @@ export function PackageDetail() {
     return <Alert variant="warning">Package not found: {name}</Alert>;
 
   const latest = versions[0];
+  const hasUnstable = versions.some((v) => v.channel === "unstable");
 
   return (
     <>
@@ -33,6 +34,14 @@ export function PackageDetail() {
 
       <CodeBlock language="bash">{`sudo dnf install ${name}`}</CodeBlock>
 
+      {hasUnstable && (
+        <div className="mt-3">
+          <CodeBlock language="bash">
+            {`# install latest unstable version\nsudo dnf --enablerepo=lair-cafe-unstable install ${name}`}
+          </CodeBlock>
+        </div>
+      )}
+
       <h2 className="mt-4 mb-3">
         Versions <Badge bg="secondary">{versions.length}</Badge>
       </h2>
@@ -41,6 +50,7 @@ export function PackageDetail() {
         <thead>
           <tr>
             <th>Version</th>
+            <th>Channel</th>
             <th>Size</th>
             <th>Built</th>
             <th>Download</th>
@@ -48,14 +58,19 @@ export function PackageDetail() {
         </thead>
         <tbody>
           {versions.map((pkg) => (
-            <tr key={`${pkg.version}-${pkg.release}`}>
+            <tr key={`${pkg.version}-${pkg.release}-${pkg.channel}`}>
               <td>
                 {pkg.version}-{pkg.release}
               </td>
+              <td>
+                <Badge bg={pkg.channel === "stable" ? "success" : "warning"}>
+                  {pkg.channel}
+                </Badge>
+              </td>
               <td>{formatBytes(pkg.size)}</td>
               <td>{new Date(pkg.buildTime * 1000).toLocaleDateString()}</td>
               <td>
-                <a href={`${manifest.baseUrl}/${pkg.rpmFilename}`}>
+                <a href={`${pkg.baseUrl}/${pkg.rpmFilename}`}>
                   {pkg.rpmFilename}
                 </a>
               </td>