Phases 11, 12: mcrctl CLI tool and mcr-web UI

Phase 11 implements the admin CLI with dual REST/gRPC transport,
global flags (--server, --grpc, --token, --ca-cert, --json), and
all commands: status, repo list/delete, policy CRUD, audit tail,
gc trigger/status/reconcile, and snapshot.

Phase 12 implements the HTMX web UI with chi router, session-based
auth (HttpOnly/Secure/SameSite=Strict cookies), CSRF protection
(HMAC-SHA256 signed double-submit), and pages for dashboard,
repositories, manifest detail, policy management, and audit log.

Security: CSRF via signed double-submit cookie, session cookies
with HttpOnly/Secure/SameSite=Strict, TLS 1.3 minimum on all
connections, form body size limits via http.MaxBytesReader.

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

web/templates/repositories.html

@@ -0,0 +1,36 @@
+{{define "title"}}Repositories{{end}}
+
+{{define "content"}}
+<h1>Repositories</h1>
+
+{{if .Error}}
+<div class="error">{{.Error}}</div>
+{{end}}
+
+{{if .Repositories}}
+<table>
+    <thead>
+        <tr>
+            <th>Name</th>
+            <th>Tags</th>
+            <th>Manifests</th>
+            <th>Size</th>
+            <th>Created</th>
+        </tr>
+    </thead>
+    <tbody>
+        {{range .Repositories}}
+        <tr>
+            <td><a href="/repositories/{{.Name}}">{{.Name}}</a></td>
+            <td>{{.TagCount}}</td>
+            <td>{{.ManifestCount}}</td>
+            <td>{{formatSize .TotalSize}}</td>
+            <td>{{formatTime .CreatedAt}}</td>
+        </tr>
+        {{end}}
+    </tbody>
+</table>
+{{else}}
+<p>No repositories found.</p>
+{{end}}
+{{end}}