feat(v1.1.7-email-outbound): SMTP send/send_html

Outbound email reachable from scripts as email::send(#{...}) (plain
text) and email::send_html(#{...}) (multipart text + HTML). Backed by a
lettre SMTP relay configured from PICLOUD_SMTP_HOST/PORT/USER/PASSWORD/
TLS/TIMEOUT_SECS; if HOST/USER/PASSWORD aren't all set the service runs
in disabled mode (every send throws NotConfigured, warned at startup).

- EmailService trait + OutboundEmail DTO (picloud-shared);
  EmailServiceImpl + EmailTransport seam + lettre transport
  (manager-core), wired into the Services bundle and Rhai engine.
- Capability::AppEmailSend (→ script:write); seven-scope commitment held.
- Required-field + RFC5322-ish address validation; 25 MB per-message cap
  (PICLOUD_EMAIL_MAX_MESSAGE_BYTES). reply_to defaults to from.
- Per-call connection (pooling deferred to v1.2); no per-app from
  validation (operator's SMTP/SPF/DKIM concern).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/executor-core/tests/sdk_docs.rs

@@ -231,6 +231,7 @@ fn make_engine() -> Arc<Engine> {
         Arc::new(picloud_shared::NoopFilesService),
         Arc::new(picloud_shared::NoopPubsubService),
         Arc::new(picloud_shared::NoopSecretsService),
+        Arc::new(picloud_shared::NoopEmailService),
     );
     Arc::new(Engine::new(Limits::default(), services))
 }