fix(audit-2026-06-11/H-1): request-body ceilings (Caddy proxy + email-inbound webhook)

- Caddy request_body { max_size 12MB } in both Caddyfiles — a hard
  ceiling replacing Caddy's multi-GB default; 12MB clears the
  orchestrator's 10 MiB user-route read. Validated with caddy validate.
- email-inbound router gets an explicit DefaultBodyLimit::max(1MB):
  the public unauthenticated webhook previously rode Axum's 2MB
  extractor default; tightened so a flood can't force large
  allocation + JSON parse per request.

Admin / execute handlers keep Axum's 2MB extractor default (already
bounded); the user-route path keeps its explicit 10 MiB manual read.

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

crates/manager-core/src/email_inbound_api.rs

@@ -169,12 +169,20 @@ pub struct EmailInboundState {
     pub bad_sig_limiter: Arc<BadSignatureLimiter>,
 }
 
+/// Per-request body cap for the inbound webhook. Inbound email events
+/// are small JSON envelopes (from/to/subject/body); 1 MiB is generous.
+/// Audit 2026-06-11 (H-1) — this public, unauthenticated endpoint
+/// otherwise rode Axum's 2 MB extractor default; pin it explicitly and
+/// tighter so a flood can't force large allocations + JSON parses.
+const INBOUND_BODY_LIMIT_BYTES: usize = 1024 * 1024;
+
 pub fn email_inbound_router(state: EmailInboundState) -> Router {
     Router::new()
         .route(
             "/email-inbound/{app_id}/{trigger_id}",
             post(receive_inbound_email),
         )
+        .layer(axum::extract::DefaultBodyLimit::max(INBOUND_BODY_LIMIT_BYTES))
         .with_state(state)
 }