Skillscript

Follow-ups that make the secured-mode migration legible, plus an optional
access gate for the dashboard.

• The approval queue now surfaces the legacy corpus. skill_list entries
  carry a gate_ok flag (computed from the source already loaded to parse — no
  extra I/O), so the dashboard Approvals tab shows not just Draft skills
  but every Approved skill the gate refuses — i.e. a pre-secured v1-stamped
  corpus, badged "re-approval needed." Each drops out of the tab as it's
  re-signed. The tab becomes a migration worklist that empties as you work it.
• Secured-mode startup warning. When the runtime starts in secured mode it
  scans the store and warns once if any skill is Approved-but-unsigned, pointing
  at skillfile reapprove --apply — so the operator isn't discovering refusals
  skill-by-skill. Best-effort; never blocks startup.
• Optional dashboard access gate. SKILLSCRIPT_DASHBOARD_AUTH_TOKEN gates
  the dashboard SPA + /rpc behind a shared secret — presented via ?token=
  (browser entry sets a session cookie), the skillscript_dash cookie, or
  Authorization: Bearer. Default unset → open (localhost bind, as before).
  This is network/casual hygiene for binding beyond localhost; the dashboard
  holds no signing key, so it is not an agent-forgery boundary (that remains
  key custody). /event keeps its own bearer token.