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>

package.json

@@ -10,11 +10,12 @@
   "bin": {
     "ccc-server": "bin/ccc-server.mjs",
     "ccc-client": "bin/ccc-client.mjs",
-    "ccc-queue":  "bin/ccc-queue.mjs",
+    "ccc-queue": "bin/ccc-queue.mjs",
     "ccc-keygen": "bin/ccc-keygen.mjs"
   },
   "dependencies": {
     "blessed": "^0.1.81",
-    "express": "^5.2.1"
+    "express": "^5.2.1",
+    "nodemailer": "^8.0.2"
   }
 }