feat(demo): plain-language integration status, richer audit, reset integrity

Integration status badges across Dashboard/Automation now show honest
plain-language labels instead of raw backend state strings (and fix a
few states that had no matching CSS colour class at all). Audit trail
gets a "view related events" action reusing the existing correlation_id
filter. About page gains scope/architecture/security/testing sections
and a guided-demo entry point. POST /api/v1/demo/reset now runs and
records a server-side scenario-integrity check. Also fixes a second real
race condition (caught by the return-review e2e test): the odometer
scenario pre-fill now resolves before ReturnForm mounts instead of
patching its value in after the fact.

frontend/src/styles.css

@@ -231,6 +231,9 @@ details summary { cursor: pointer; color: var(--teal-dark); }.data-table details
 .about-card h2 { margin: 0 0 8px; color: var(--ink); font-size: 1rem; letter-spacing: -.015em; }
 .about-card p { margin: 0; color: var(--muted); font-size: .82rem; line-height: 1.62; }
 .about-card p code { padding: 1px 5px; background: var(--surface-subtle); border-radius: 4px; font-size: .78rem; }
+.about-cta { display: flex; align-items: center; justify-content: space-between; gap: 16px; flex-wrap: wrap; background: var(--teal-pale); border-color: #bfe6df; }
+.about-cta strong { display: block; color: var(--ink); font-size: .85rem; }
+.about-cta p { margin: 2px 0 0; }
 .detail-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(180px, 1fr)); gap: 1px; margin: 0; background: var(--line); border: 1px solid var(--line); }
 .detail-grid div { min-height: 76px; padding: 13px 14px; background: white; }
 .detail-grid dt { margin: 0; color: var(--muted); font-size: .63rem; font-weight: 700; text-transform: uppercase; letter-spacing: .065em; }.detail-grid dd { margin: 7px 0 0; color: var(--ink); font-size: .82rem; font-weight: 700; }
@@ -249,6 +252,8 @@ details summary { cursor: pointer; color: var(--teal-dark); }.data-table details
 .commit-list { list-style: none; display: grid; gap: 7px; margin: 16px 0 0; padding: 0; color: var(--muted); font-size: .7rem; }.commit-list li { display: flex; gap: 7px; }.commit-list svg { width: 14px; color: var(--teal-dark); }
 .success-panel { padding: 22px; }.result-heading { display: flex; align-items: center; gap: 12px; margin-bottom: 18px; }.result-heading > span { width: 40px; height: 40px; display: grid; place-items: center; color: white; background: var(--success); border-radius: 50%; }.result-heading svg { width: 20px; }.result-heading h2 { margin: 0; font-size: 1.2rem; }
 .result-links { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 16px; }
+.link-button { padding: 0; color: var(--teal-dark); background: transparent; border: 0; font-size: inherit; font-weight: 700; text-decoration: underline; cursor: pointer; }
+.link-button:hover { color: var(--teal); }
 .rule-explainer { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 14px; margin-bottom: 18px; padding: 16px 18px; background: var(--info-pale); border: 1px solid #cfe3ee; border-radius: var(--radius); }
 .rule-explainer strong { display: block; margin-bottom: 4px; color: var(--ink); font-size: .72rem; font-weight: 700; text-transform: uppercase; letter-spacing: .05em; }
 .rule-explainer p { margin: 0; color: var(--ink-soft); font-size: .78rem; line-height: 1.55; }