docs(modules): add client manifest generation and update discovery docs

- introduce `OUTPUT_CLIENT` constant and `renderClientManifest` for `'use client'` bundle
- rename `renderManifest` to `renderServerManifest` for clarity
- update `sync` command to write both server and client manifests
- update `findInstalledModuleNames` to support custom package path resolution
- rewrite MODULES.md to explain dual-manifest architecture and client hydration rationale

src/core/modules/cli.js

@@ -20,7 +20,8 @@ import { resolve, dirname } from 'node:path';
 import { step, done, warn, fail } from '@zen/core/shared/logger';
 import { findInstalledModuleNames } from './discover.server.js';
 
-const OUTPUT_PATH = 'app/.zen/modules.generated.js';
+const OUTPUT_SERVER = 'app/.zen/modules.generated.js';
+const OUTPUT_CLIENT = 'app/.zen/modules.client.js';
 
 function safeIdentifier(name, idx) {
   // `@zen/module-posts` → `m0_zen_module_posts`
@@ -28,7 +29,7 @@ function safeIdentifier(name, idx) {
   return `m${idx}_${cleaned}`;
 }
 
-function renderManifest(names) {
+function renderServerManifest(names) {
   const header = '// AUTO-GÉNÉRÉ par `npx zen-modules sync` — ne pas modifier à la main.\n';
 
   if (names.length === 0) {
@@ -52,12 +53,48 @@ function renderManifest(names) {
     '];',
     '',
     '// Top-level await : déclenche register() de chaque module au moment de l\'import',
-    '// de ce manifeste, des deux côtés (server bundle + client bundle).',
+    '// côté serveur. instrumentation.js importe ce fichier au boot.',
     'await Promise.all(modules.map(m => m.exports.register?.()));',
     '',
   ].join('\n');
 }
 
+function renderClientManifest(names) {
+  // Doit être un Client Component pour que les side-effects (registerPage, etc.)
+  // s\'exécutent dans le bundle browser au moment de l\'hydratation. app/layout.js
+  // (Server Component) importe ce fichier ; Next.js bascule sur le bundle client
+  // et exécute les register() lors du chargement de la page.
+  const header = [
+    '// AUTO-GÉNÉRÉ par `npx zen-modules sync` — ne pas modifier à la main.',
+    "'use client';",
+    '',
+  ].join('\n');
+
+  if (names.length === 0) {
+    return header + '\nexport {};\n';
+  }
+
+  const imports = names
+    .map((name, i) => `import * as ${safeIdentifier(name, i)} from '${name}';`)
+    .join('\n');
+
+  const calls = names
+    .map((_, i) => `${safeIdentifier(names[i], i)}.register?.();`)
+    .join('\n');
+
+  return [
+    header,
+    imports,
+    '',
+    '// Fire and forget — registerPage/registerWidget sont synchrones, le reste',
+    '// (init asynchrone éventuel) ne bloque pas le rendu.',
+    calls,
+    '',
+    'export {};',
+    '',
+  ].join('\n');
+}
+
 async function readIfExists(path) {
   try {
     return await readFile(path, 'utf-8');
@@ -66,20 +103,31 @@ async function readIfExists(path) {
   }
 }
 
+async function writeIfChanged(path, contents) {
+  const prev = await readIfExists(path);
+  if (prev === contents) return false;
+  await mkdir(dirname(path), { recursive: true });
+  await writeFile(path, contents, 'utf-8');
+  return true;
+}
+
 async function syncCommand({ cwd = process.cwd() } = {}) {
   const names = await findInstalledModuleNames({ cwd });
-  const outputPath = resolve(cwd, OUTPUT_PATH);
-  const next = renderManifest(names);
-  const prev = await readIfExists(outputPath);
+  const count = `(${names.length} module${names.length === 1 ? '' : 's'})`;
 
-  if (prev === next) {
-    step(`zen-modules: ${OUTPUT_PATH} already up to date (${names.length} module${names.length === 1 ? '' : 's'})`);
+  const serverPath = resolve(cwd, OUTPUT_SERVER);
+  const clientPath = resolve(cwd, OUTPUT_CLIENT);
+
+  const wroteServer = await writeIfChanged(serverPath, renderServerManifest(names));
+  const wroteClient = await writeIfChanged(clientPath, renderClientManifest(names));
+
+  if (!wroteServer && !wroteClient) {
+    step(`zen-modules: manifests already up to date ${count}`);
     return;
   }
 
-  await mkdir(dirname(outputPath), { recursive: true });
-  await writeFile(outputPath, next, 'utf-8');
-  done(`zen-modules: wrote ${OUTPUT_PATH} (${names.length} module${names.length === 1 ? '' : 's'})`);
+  if (wroteServer) done(`zen-modules: wrote ${OUTPUT_SERVER} ${count}`);
+  if (wroteClient) done(`zen-modules: wrote ${OUTPUT_CLIENT} ${count}`);
   for (const name of names) step(`  → ${name}`);
 }
 

src/core/modules/discover.server.js

@@ -1,7 +1,7 @@
 import { readFile } from 'node:fs/promises';
 import { resolve, join } from 'node:path';
 import { createRequire } from 'node:module';
-import { warn } from '@zen/core/shared/logger';
+import { info, warn } from '@zen/core/shared/logger';
 import { registerModule } from './registry.js';
 
 /**
@@ -43,6 +43,7 @@ export function registerModules(modules) {
       createTables: ex.createTables,
       dropTables: ex.dropTables,
     });
+    info(`zen-modules: registered ${ex.manifest.name}@${ex.manifest.version ?? '?'}`);
   }
 }