feat(model-aliases): restore Fast service-tier option

- enable Fast for Codex API, OpenAI-compatible, and Codex OAuth sources
- apply service_tier=priority as an independent payload override
- support Fast-only and reasoning-effort combinations
- disable Fast until a supported model source is selected

src/styles.css

@@ -4788,6 +4788,70 @@ textarea:focus-visible {
   opacity: 0.45;
 }
 
+.thinking-fast-option {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+  width: 100%;
+  min-height: 48px;
+  padding: 8px 10px;
+  border: 1px solid var(--theme-d5d2cb);
+  border-radius: 7px;
+  background: var(--theme-fff);
+  color: var(--theme-7a746c);
+  cursor: pointer;
+  transition: border-color 140ms ease, background 140ms ease, color 140ms ease;
+}
+
+.thinking-fast-option:hover {
+  border-color: var(--theme-d7a447);
+}
+
+.thinking-fast-option.active {
+  border-color: var(--theme-d7a447);
+  background: var(--theme-fff8eb);
+  color: var(--theme-805a24);
+}
+
+.thinking-fast-option-copy {
+  display: grid;
+  min-width: 0;
+  gap: 2px;
+}
+
+.thinking-fast-option-copy > span {
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  font-size: var(--font-size-section);
+  font-weight: 800;
+}
+
+.thinking-fast-option-copy small {
+  color: var(--theme-9a938a);
+  font-size: var(--font-size-label);
+}
+
+.thinking-fast-option.active .thinking-fast-option-copy small {
+  color: var(--theme-805a24);
+}
+
+.thinking-fast-option:has(input:disabled) {
+  cursor: not-allowed;
+  opacity: 0.55;
+}
+
+.thinking-fast-switch {
+  width: 42px;
+  height: 23px;
+}
+
+.thinking-fast-switch input:checked + .switch-track {
+  border-color: var(--theme-d7a447);
+  background: var(--theme-d7a447);
+}
+
 .thinking-alias-input {
   width: 100%;
   height: 36px;
@@ -4985,6 +5049,12 @@ textarea:focus-visible {
   text-transform: none;
 }
 
+.thinking-effort-badge.fast {
+  border-color: var(--theme-d7a447);
+  background: var(--theme-fff8eb);
+  color: var(--theme-805a24);
+}
+
 @media (min-width: 1081px) {
   .thinking-alias-list-panel .thinking-alias-row {
     grid-template-columns: minmax(0, 1fr) auto 34px;