refactor(frontend): CSS pay-down, derive batch (milestone 302 step 4) — page-header, error-msg/state-msg/empty-msg, empty-title/empty-sub, required, field-hint recipes into components.css; form-buttons into rules-shared.css; scoped copies trimmed to remainders/overrides; the three views' .input becomes fs-input + width/box-sizing remainder (canon #2336)

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

frontend/src/components/InceptionCard.vue

@@ -185,5 +185,4 @@ onMounted(load);
   font-size: 0.9rem;
 }
 .inception-actions { display: flex; justify-content: flex-end; margin-top: 0.5rem; }
-.error-msg { color: var(--fs-error); font-size: 0.9rem; }
 </style>

frontend/src/components/SystemsSection.vue

@@ -484,10 +484,10 @@ async function confirmDelete() {
   border: 1px dashed var(--fs-border-color);
   border-radius: var(--fs-radius-lg);
 }
-.empty-title { margin: 0; font-weight: 500; color: var(--fs-text-primary); }
-.empty-sub { margin: 0 0 0.5rem; font-size: 0.82rem; color: var(--fs-text-tertiary); max-width: 32ch; }
+/* remainders over the shared recipes (components.css, m302) */
+.empty-title { margin: 0; color: var(--fs-text-primary); }
+.empty-sub { margin: 0 0 0.5rem; font-size: 0.82rem; max-width: 32ch; }
 
-.error-msg { color: var(--fs-error); font-size: 0.9rem; }
 
 /* ── Skeleton ─────────────────────────────────────────────────── */
 @keyframes skel-shine { to { background-position: 200% center; } }