feat(ui): auth-gate the landing, add Help page and Home nav

- Landing shows the tool tiles only when signed in and a sign-in card
  otherwise; the login callback now returns to /.
- New public /help page: intro plus a per-tool Carbon accordion.
- Nav restructured to Home, {services}, divider, Help, Sign In/Out in
  both the header and the side nav; the header right keeps only the
  identity chip. Side-nav logo enlarged, border removed, spacing
  equalised. Sign-out modal no longer flashes before it is defined.
- Per-deploy asset versioning (?v=) with immutable asset caching and
  no-store HTML; help step lists show their numbers again.
- Tests updated and extended (48 total).

tools/public/assets/style.css

@@ -26,11 +26,13 @@ cds-progress-bar:not(:defined) {
 /* Carbon styles the shadow anchor inside tiles, not the host — give the host
    a real box so grid columns and click targets work correctly. */
 cds-tile, cds-clickable-tile { display: block; }
+/* an undefined modal renders its header/body/footer inline — hide it until defined */
+cds-modal:not(:defined) { display: none; }
 
 /* ── header + side nav (Carbon ui-shell) ────────────────────────────────── */
 cds-header:not(:defined), cds-side-nav:not(:defined) { visibility: hidden; }
 .brand-inner { display: inline-flex; align-items: center; gap: 0.5rem; }
-.brand-logo { display: inline-flex; align-items: center; justify-content: center; border: 1px solid var(--cds-border-subtle, #e0e0e0); border-radius: 4px; padding: 2px; }
+.brand-logo { display: inline-flex; align-items: center; justify-content: center; }
 .brand-logo img { display: block; }
 .brand-suffix { color: var(--cds-text-secondary, #525252); font-weight: 400; }
 
@@ -61,13 +63,13 @@ cds-side-nav[expanded] { pointer-events: auto; }
 }
 .user-chip { display: inline-flex; align-items: center; gap: 0.45rem; color: var(--cds-text-primary, #161616); font-size: 13px; }
 .user-chip .avatar { width: 26px; height: 26px; border-radius: 50%; background: #0f62fe; color: #fff; display: inline-flex; align-items: center; justify-content: center; font-size: 11px; font-weight: 700; }
-.linklike { background: none; border: none; padding: 0; color: var(--cds-link-primary, #0f62fe); font-weight: 400; cursor: pointer; font-size: 13px; font-family: inherit; }
-.linklike:hover { color: var(--cds-link-primary-hover, #0043ce); text-decoration: underline; }
-.linklike[disabled] { color: var(--cds-text-disabled, #c6c6c6); cursor: default; }
 
 /* logo above the mobile side-nav items */
-.side-nav-brand { display: flex; align-items: center; gap: 0.75rem; padding: 1rem; color: var(--cds-text-primary, #161616); font-weight: 600; font-size: 14px; border-bottom: 1px solid var(--cds-border-subtle, #e0e0e0); }
-.side-nav-brand img { border: 1px solid var(--cds-border-subtle, #e0e0e0); border-radius: 6px; padding: 2px; display: block; }
+.side-nav-brand { display: flex; align-items: center; gap: 0.75rem; padding: 2rem 1rem 1rem; color: var(--cds-text-primary, #161616); font-weight: 600; font-size: 14px; }
+.side-nav-brand img { display: block; }
+
+/* separator between the service links and Help in the header nav */
+.header-nav-divider { width: 1px; align-self: stretch; margin: 0.7rem 0.25rem; background: var(--cds-border-subtle, #e0e0e0); }
 
 /* ── layout ─────────────────────────────────────────────────────────────── */
 .container { width: 100%; max-width: 1136px; margin: 0 auto; padding: 0 1.5rem; }
@@ -114,6 +116,14 @@ main.container { flex: 1 0 auto; padding-top: 1.5rem; padding-bottom: 1.5rem; }
 .tool-card .go { margin-top: auto; color: var(--cds-link, #0f62fe); font-weight: 600; font-size: 13px; display: inline-flex; align-items: center; gap: 0.3rem; }
 .tool-card .go svg { width: 14px; height: 14px; }
 
+/* ── help page ──────────────────────────────────────────────────────────── */
+cds-accordion { display: block; max-width: 720px; }
+.help-intro { max-width: 720px; color: var(--cds-text-secondary, #525252); margin: 0 0 1.5rem; font-size: 14px; }
+.help-steps { list-style: decimal; padding-left: 1.25rem; margin: 0.5rem 0; }
+.help-steps li { margin-bottom: 0.35rem; }
+.help-steps li::marker { color: var(--cds-text-secondary, #525252); }
+.help-note { color: var(--cds-text-secondary, #525252); font-size: 13px; max-width: 720px; }
+
 /* ── forms (Carbon-styled native controls) ──────────────────────────────── */
 label { font-weight: 400; font-size: 12px; color: var(--cds-text-secondary, #525252); margin-bottom: 0.25rem; display: block; }
 .form-control {
@@ -131,9 +141,10 @@ textarea.form-control { height: auto; padding: 0.6rem 0.75rem; }
 .btn {
   border-radius: 0; font-weight: 400; font-size: 14px;
   padding: 0.65rem 0.95rem; border: 1px solid transparent;
-  text-decoration: none; display: inline-block; cursor: pointer;
+  text-decoration: none; display: inline-flex; align-items: center; justify-content: center; gap: 0.5rem; cursor: pointer;
   font-family: inherit; line-height: 1.2; text-align: center;
 }
+.btn svg { width: 16px; height: 16px; flex-shrink: 0; }
 .btn-primary { background: var(--cds-button-primary, #0f62fe); border-color: var(--cds-button-primary, #0f62fe); color: #fff; }
 .btn-primary:hover, .btn-primary:focus { background: #0353e9; border-color: #0353e9; color: #fff; }
 .btn-ghost { background: transparent; border-color: var(--cds-border-strong, #8d8d8d); color: var(--cds-text-primary, #161616); }
@@ -196,4 +207,5 @@ footer.foot a { color: var(--cds-text-secondary, #525252); }
 .message-card h1 { font-size: 1.25rem; font-weight: 600; margin: 0; }
 .message-icon { width: 52px; height: 52px; border-radius: 50%; display: inline-flex; align-items: center; justify-content: center; background: var(--cds-support-error, #da1e28); color: #fff; margin-bottom: 0.4rem; }
 .message-icon.error svg { width: 24px; height: 24px; }
+.message-icon.info { background: var(--cds-button-primary, #0f62fe); }
 .message-card .btn { margin-top: 0.6rem; min-width: 200px; }