panel-redesign: Sign in and Create administrator on the kit

Stage 2, step 1. Written by Sonnet, reviewed by Opus.

  - templates/login.html, setup.html: written from the mockups as the
    content of layout_signed_out - form.sp-form, kicker, h1, Bulma fields
    with icons, the full-width primary button. Actions, field names,
    autocomplete and autofocus are the old ones.
  - view/signin.go: typed Login and Setup (Meta carries a title only, so
    Engine.Render takes the signed-out layout); auth handlers pass them
    instead of maps.
  - login and setup are in kitPages, have fixtures, and are off
    legacy_pages.txt.

States the mockups do not draw:
  - a refused sign-in / setup is the kit's flash (notification is-danger
    is-light) above the fields;
  - login before any administrator exists shows the old sentence in a
    form.sp-form that has no action and no control: the signed-out
    stylesheet sizes and centres its column through "form" alone. A
    workaround, listed for the owner.

Differences from the mockups, for the owner:
  - the kicker is <p><span class="sp-kicker"> (the kit's partial is a
    span; a page may not write the class), the mockup has <p
    class="sp-kicker">: the block sits about 3px lower;
  - login's kicker is the configured host name and is absent when there
    is none; setup's is the mockup's fixed text;
  - the footer is the layout's legal line (full copyright holder name);
  - the user name field has autofocus, so it shows its focus ring.

Evidence
  - docs/assets/panel-redesign/evidence/login.png, setup.png: 1440x900,
    headless Edge, from the real templates served locally with their
    fixtures - NOT from the container (no Docker on this machine).
  - panel/audit.js on login, login with an error, login without an
    administrator, setup, setup with an error, at 1440 and 1280:
    118 texts checked, problems: [] ; no page is taller than 900px.
  - go test -count=1 ./internal/web/...
      ok  internal/web
      ok  internal/web/auth
      ok  internal/web/handlers
      ok  internal/web/validate
      ok  internal/web/view

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/view/legacy_pages.txt

@@ -23,10 +23,8 @@ help
 inbound
 inbound_delete
 inbound_domain
-login
 mail_queue
 settings
-setup
 status
 system_log
 user_delete