feat: implemented plugin configuration UI and calendar event action slot

- Add configSchema support to plugin manifest and ServerPlugin registry
- Add schema-driven admin config page (string, secret, boolean, number, select fields)
- Add per-plugin config storage backend (JSON files + REST API)
- Add calendar-event-actions and admin-plugin-page slot names to plugin store
- Add registerCalendarEventAction and registerAdminPage to plugin API
- Add calendarFormHooks (onCalendarEventFormOpen/Save) to hook bus
- Add PluginSlot in calendar event modal for plugin action buttons
- Style calendar event action buttons to match Bulwark outline button design
- Add Configure link per plugin in admin plugins dashboard
- Add Jitsi Meet plugin with tests (repos/plugins/jitsi-meet)
- Exclude data/admin/plugins from ESLint (deployed plugin bundles)

lib/admin/plugin-config.ts

@@ -0,0 +1,81 @@
+import { readFile, writeFile, mkdir, rename, unlink } from 'node:fs/promises';
+import { existsSync } from 'node:fs';
+import path from 'node:path';
+import { logger } from '@/lib/logger';
+
+function getAdminDir(): string {
+  return process.env.ADMIN_DATA_DIR || path.join(process.cwd(), 'data', 'admin');
+}
+
+function getPluginConfigDir(): string {
+  return path.join(getAdminDir(), 'plugin-config');
+}
+
+function configPath(pluginId: string): string {
+  return path.join(getPluginConfigDir(), `${pluginId}.json`);
+}
+
+async function ensureDir(dir: string): Promise<void> {
+  if (!existsSync(dir)) {
+    await mkdir(dir, { recursive: true });
+  }
+}
+
+/**
+ * Get all config for a plugin.
+ */
+export async function getPluginConfig(pluginId: string): Promise<Record<string, unknown>> {
+  try {
+    const raw = await readFile(configPath(pluginId), 'utf-8');
+    return JSON.parse(raw);
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === 'ENOENT') return {};
+    logger.warn(`Failed to read plugin config for ${pluginId}`, {
+      error: error instanceof Error ? error.message : 'Unknown error',
+    });
+    return {};
+  }
+}
+
+/**
+ * Set a single config key for a plugin.
+ */
+export async function setPluginConfig(pluginId: string, key: string, value: unknown): Promise<void> {
+  const dir = getPluginConfigDir();
+  await ensureDir(dir);
+
+  const config = await getPluginConfig(pluginId);
+  config[key] = value;
+
+  const filePath = configPath(pluginId);
+  const tmpPath = filePath + '.tmp';
+  await writeFile(tmpPath, JSON.stringify(config, null, 2), 'utf-8');
+  await rename(tmpPath, filePath);
+}
+
+/**
+ * Delete a single config key for a plugin.
+ */
+export async function deletePluginConfigKey(pluginId: string, key: string): Promise<void> {
+  const config = await getPluginConfig(pluginId);
+  delete config[key];
+
+  if (Object.keys(config).length === 0) {
+    try { await unlink(configPath(pluginId)); } catch { /* ok if missing */ }
+    return;
+  }
+
+  const dir = getPluginConfigDir();
+  await ensureDir(dir);
+  const filePath = configPath(pluginId);
+  const tmpPath = filePath + '.tmp';
+  await writeFile(tmpPath, JSON.stringify(config, null, 2), 'utf-8');
+  await rename(tmpPath, filePath);
+}
+
+/**
+ * Delete all config for a plugin (used when uninstalling).
+ */
+export async function deleteAllPluginConfig(pluginId: string): Promise<void> {
+  try { await unlink(configPath(pluginId)); } catch { /* ok if missing */ }
+}