feat(dashboard): onboarding wizard UI (#123-127)

A dedicated multi-step onboarding flow at /onboard (new "Onboard" sidebar entry),
wired to the #131 target endpoints:
- Step 1 — target type: card grid of the 9 families + name.
- Step 2 — artifacts: type-aware add-a-row form (git/live-url/firmware/mobile/
  container/PLC/archive/text) with a removable list.
- Step 3 — review: summary of type + artifacts.
- Step 4 — done: creates the target, runs kind-based detection, and shows the
  applicable-scans matrix (default-on / blocked with rationale).

Server fns in infrastructure/onboarding.rs proxy to /api/v1/targets (create,
detect, applicable-scans). Compiles clean under both --features web and
--features server; fmt + clippy -D warnings pass.

Full scan-selection toggling and a "launch scan" action are follow-ups (launch
needs the unified pipeline, #133).

Closes #123, #124, #125. Refs #126, #127, #118.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

compliance-dashboard/src/infrastructure/mod.rs

@@ -10,6 +10,7 @@ pub mod issues;
 pub mod mcp;
 pub mod mcp_tokens;
 pub mod notifications;
+pub mod onboarding;
 pub mod pentest;
 #[allow(clippy::too_many_arguments)]
 pub mod repositories;