website: fix nine review findings (generator coverage, loader facts, mode semantics)

Generator (all four structural gaps):
- harness service pages now render public properties/accessors, not just
  methods (ctx.codeRuntime.language/isolation were missing);
- the class page merges the same-named interface half, so ctx.root/baseUrl/
  events/logger/reflect/registry appear on Context (vendor root JSDoc gains
  prose alongside @experimental);
- Pick<…> heritage on a Context merge resolves to the picked class members,
  giving ctx.effect a documented signature on the Fiber page;
- {@link} tags normalize to code spans; merge sections get their own h2 so
  reflect members no longer nest under 'Static members'.

verify-website-yaml: reject the unloadable 'group:' pseudo-name (tree.import
only special-cases 'cordis:'; no builtin is registered here) and recurse into
@cordisjs/plugin-group nested entry lists instead.

Prose corrected against loader/cordis source: service.md isolation example
uses the real group plugin + group: true + the required isolate map;
config.md documents concurrent entry startup (Promise.all; order via inject)
and the real hmr defaults (root ['.'], base/ignored/debounce); events.md
fixes emit (synchronous, not parallel), bail (null/false also delegate), and
serial (stops at the first bail value).

scripts/verify-website-yaml.ts

@@ -201,8 +201,15 @@ function checkEntryList(
     }
     // Illustrative local plugin — nothing on disk to check against.
     if (name.startsWith('./') || name.startsWith('../')) return
-    // Loader built-in group: its config is a nested entry list.
+    // A `group:`-style pseudo-name is NOT loadable: tree.import() only
+    // special-cases the `cordis:` prefix, and nothing in this repo registers
+    // loader builtins — reject it and point at the real group plugin.
     if (name.startsWith('group:')) {
+      flag(`${at}: \`${name}\` is not loadable (no loader builtin is registered); use \`@cordisjs/plugin-group\` with \`group: true\``)
+      return
+    }
+    // The vendored group plugin: its config is a nested entry list.
+    if (name === '@cordisjs/plugin-group') {
       if (Array.isArray(entry['config'])) checkEntryList(entry['config'], known, block, violations)
       return
     }