feat: add task assignment

frontend/src/styles.css

@@ -23,6 +23,7 @@ h1 {
 
 button,
 input,
+select,
 textarea {
   font: inherit;
 }
@@ -38,6 +39,7 @@ button {
 
 button:disabled,
 input:disabled,
+select:disabled,
 textarea:disabled {
   cursor: not-allowed;
   opacity: 0.65;
@@ -70,6 +72,15 @@ input {
   border-radius: 0.4rem;
 }
 
+select {
+  box-sizing: border-box;
+  width: 100%;
+  padding: 0.6rem;
+  border: 1px solid #9ca3af;
+  border-radius: 0.4rem;
+  background: white;
+}
+
 textarea {
   box-sizing: border-box;
   width: 100%;
@@ -174,6 +185,68 @@ textarea {
   margin: 0;
 }
 
+.task-assignment {
+  margin-top: 0.9rem;
+}
+
+.task-assignee {
+  display: inline-flex;
+  align-items: center;
+  gap: 0.4rem;
+  color: #475569;
+  font-size: 0.9rem;
+}
+
+.task-assignee-button {
+  padding: 0.25rem 0;
+  color: #2563eb;
+  background: transparent;
+}
+
+.task-assignee-static {
+  margin-top: 0.9rem;
+}
+
+.user-icon {
+  flex: 0 0 auto;
+}
+
+.assignee-select-label {
+  display: flex;
+  align-items: center;
+  gap: 0.4rem;
+}
+
+.assignee-select-label select {
+  width: auto;
+  min-width: 9rem;
+}
+
+.assignment-error {
+  margin-top: 0.4rem;
+  font-size: 0.85rem;
+}
+
+.field-label-uppercase {
+  color: #64748b;
+  font-size: 0.8rem;
+  font-weight: 700;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+}
+
+.visually-hidden {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border: 0;
+}
+
 .task-card-header {
   display: flex;
   align-items: flex-start;