docs: add ARCHITECTURE.md and AGENTS.md, split CSS, fix justfile

- Add ARCHITECTURE.md with full system overview (data flow, modules, build)
- Add AGENTS.md as a guide for future AI agents working on this project
- Split monolithic styles.css into focused files under assets/:
  variables, animations, layout, navbar, header, cards, config,
  filters, utils, greet
- Fix justfile: replace `cargo run tauri dev/build` with `cargo tauri dev/build`

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/utils.css

@@ -0,0 +1,65 @@
+/* --- Utility & State Classes --- */
+.reload-btn-large {
+    cursor: pointer;
+    background: linear-gradient(
+        135deg,
+        rgba(74, 144, 226, 0.15),
+        rgba(74, 144, 226, 0.05)
+    );
+    color: var(--accent-color);
+    padding: 16px;
+    border-radius: 16px;
+    width: 100%;
+    font-weight: 700;
+    border: 1px solid rgba(74, 144, 226, 0.3);
+    user-select: none;
+    min-height: 52px;
+    transition: all 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    gap: 10px;
+    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
+}
+
+.reload-btn-large:hover {
+    background: rgba(74, 144, 226, 0.2);
+    border-color: var(--accent-color);
+    box-shadow: 0 6px 20px rgba(74, 144, 226, 0.2);
+    transform: translateY(-2px);
+}
+
+.reload-btn-large:active {
+    transform: scale(0.96) translateY(0);
+}
+
+.error-box {
+    background: rgba(239, 68, 68, 0.1);
+    border: 1px solid rgba(239, 68, 68, 0.3);
+    color: var(--danger);
+    padding: 15px;
+    border-radius: 12px;
+    text-align: center;
+}
+
+.loading-spinner {
+    text-align: center;
+    padding: 40px;
+    color: var(--text-secondary);
+    font-style: italic;
+    animation: pulse-subtle 2s infinite;
+}
+
+.empty-msg {
+    text-align: center;
+    color: var(--text-secondary);
+    margin-top: 40px;
+    font-size: 0.9rem;
+    opacity: 0.8;
+}
+
+.status-msg {
+    text-align: center;
+    color: var(--text-secondary);
+    padding: 40px 16px;
+}