Implement email support with per-user permission model (closes #2)

New modules:
- server/mailer.mjs: nodemailer transport wrapper
- server/mail_perms.mjs: runtime permission store, persisted to disk

New actions:
- send-email: checks (caller, to, topic) permission before sending
- set-mail-permission: grant/revoke permissions, gated by canApprove
- get-mail-permissions: list current permissions

Handler signature extended to handler(params, ctx) where ctx carries
caller, users, mail_perm_store and mailer_send. Existing handlers
ignore ctx so the change is backwards-compatible.

SMTP config lives in secrets.json under optional 'smtp' key.
Mail permissions path via --mail-perms or CONDUIT_MAIL_PERMS.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/actions.mjs

@@ -2,7 +2,8 @@
 // policy: "auto-accept" | "auto-deny" | "queue"
 
 
-import { resolve_path, exec } from "./helpers.mjs";
+import { resolve_path, exec } from './helpers.mjs';
+import { check_can_approve } from './auth.mjs';
 
 export const actions = {
 	"list-actions": {
@@ -67,4 +68,56 @@ export const actions = {
 			return { opened: resolved };
 		},
 	},
+
+	'send-email': {
+		description: 'Send an email to a permitted recipient',
+		params: [
+			{ name: 'to',      required: true,  type: 'string' },
+			{ name: 'subject', required: true,  type: 'string' },
+			{ name: 'body',    required: true,  type: 'string' },
+			{ name: 'topic',   required: true,  type: 'string' },
+		],
+		policy: 'auto-accept',
+		handler: async ({ to, subject, body, topic }, { caller, mail_perm_store, mailer_send }) => {
+			if (!mail_perm_store.check(caller, to, topic)) {
+				throw new Error(`Mail permission denied: ${caller} → ${to} [${topic}]`);
+			}
+			await mailer_send(to, subject, body);
+			return { sent: true, to, topic };
+		},
+	},
+
+	'set-mail-permission': {
+		description: 'Grant or revoke permission for a user to send email to a recipient/topic',
+		params: [
+			{ name: 'target_user', required: true,  type: 'string' },
+			{ name: 'to',          required: true,  type: 'string' },
+			{ name: 'topic',       required: true,  type: 'string' },
+			{ name: 'allow',       required: true,  type: 'boolean' },
+		],
+		policy: 'auto-accept',
+		handler: ({ target_user, to, topic, allow }, { caller, users, mail_perm_store }) => {
+			if (!check_can_approve(users, caller, target_user)) {
+				throw new Error(`Not authorized to set mail permissions for '${target_user}'`);
+			}
+			if (allow) {
+				mail_perm_store.add(target_user, to, topic);
+			} else {
+				mail_perm_store.remove(target_user, to, topic);
+			}
+			return { target_user, to, topic, allow, permissions: mail_perm_store.list() };
+		},
+	},
+
+	'get-mail-permissions': {
+		description: 'List current mail permissions, optionally filtered by user',
+		params: [
+			{ name: 'target_user', required: false, type: 'string' },
+		],
+		policy: 'auto-accept',
+		handler: ({ target_user }, { mail_perm_store }) => {
+			const all = mail_perm_store.list();
+			return { permissions: target_user ? all.filter(e => e.user === target_user) : all };
+		},
+	},
 };