feat: implement ReasonPrompt component with quick tags

- Create ReasonPrompt dialog for capturing optional reasons
- Add quick tag buttons (Blocking, Urgent, Context switch, etc.)
- Support keyboard navigation (Escape to cancel)
- Handle text input with trimming and null for empty
- Different titles for different actions (set_focus, defer, skip)
- All 10 tests pass

Closes bd-2p0

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/components/ReasonPrompt.test.tsx

@@ -0,0 +1,158 @@
+/**
+ * Tests for ReasonPrompt component.
+ *
+ * TDD: These tests define the expected behavior before implementation.
+ */
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { ReasonPrompt } from "@/components/ReasonPrompt";
+
+describe("ReasonPrompt", () => {
+  const defaultProps = {
+    action: "set_focus",
+    itemTitle: "Review MR !847",
+    onSubmit: vi.fn(),
+    onCancel: vi.fn(),
+  };
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("renders with action context", () => {
+    render(<ReasonPrompt {...defaultProps} />);
+
+    expect(
+      screen.getByText(/Setting focus to.*Review MR !847/i)
+    ).toBeInTheDocument();
+  });
+
+  it("captures text input", async () => {
+    const user = userEvent.setup();
+    const onSubmit = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onSubmit={onSubmit} />);
+
+    await user.type(
+      screen.getByRole("textbox"),
+      "Sarah pinged me, she is blocked"
+    );
+    await user.click(screen.getByRole("button", { name: /confirm/i }));
+
+    expect(onSubmit).toHaveBeenCalledWith(
+      expect.objectContaining({
+        reason: "Sarah pinged me, she is blocked",
+      })
+    );
+  });
+
+  it("allows selecting quick tags", async () => {
+    const user = userEvent.setup();
+    const onSubmit = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onSubmit={onSubmit} />);
+
+    await user.click(screen.getByRole("button", { name: /blocking/i }));
+    await user.click(screen.getByRole("button", { name: /urgent/i }));
+    await user.click(screen.getByRole("button", { name: /confirm/i }));
+
+    expect(onSubmit).toHaveBeenCalledWith(
+      expect.objectContaining({
+        tags: expect.arrayContaining(["blocking", "urgent"]),
+      })
+    );
+  });
+
+  it("toggles tag off when clicked again", async () => {
+    const user = userEvent.setup();
+    const onSubmit = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onSubmit={onSubmit} />);
+
+    const blockingTag = screen.getByRole("button", { name: /blocking/i });
+
+    // Select then deselect
+    await user.click(blockingTag);
+    await user.click(blockingTag);
+    await user.click(screen.getByRole("button", { name: /confirm/i }));
+
+    expect(onSubmit).toHaveBeenCalledWith(
+      expect.objectContaining({
+        tags: [],
+      })
+    );
+  });
+
+  it("allows skipping reason", async () => {
+    const user = userEvent.setup();
+    const onSubmit = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onSubmit={onSubmit} />);
+
+    await user.click(screen.getByRole("button", { name: /skip reason/i }));
+
+    expect(onSubmit).toHaveBeenCalledWith({
+      reason: null,
+      tags: [],
+    });
+  });
+
+  it("trims whitespace from reason", async () => {
+    const user = userEvent.setup();
+    const onSubmit = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onSubmit={onSubmit} />);
+
+    await user.type(screen.getByRole("textbox"), "  spaced reason  ");
+    await user.click(screen.getByRole("button", { name: /confirm/i }));
+
+    expect(onSubmit).toHaveBeenCalledWith(
+      expect.objectContaining({
+        reason: "spaced reason",
+      })
+    );
+  });
+
+  it("treats empty reason as null", async () => {
+    const user = userEvent.setup();
+    const onSubmit = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onSubmit={onSubmit} />);
+
+    // Just click confirm without typing
+    await user.click(screen.getByRole("button", { name: /confirm/i }));
+
+    expect(onSubmit).toHaveBeenCalledWith(
+      expect.objectContaining({
+        reason: null,
+      })
+    );
+  });
+
+  it("cancels on Escape key", async () => {
+    const user = userEvent.setup();
+    const onCancel = vi.fn();
+    render(<ReasonPrompt {...defaultProps} onCancel={onCancel} />);
+
+    await user.keyboard("{Escape}");
+
+    expect(onCancel).toHaveBeenCalled();
+  });
+
+  it("displays all quick tag options", () => {
+    render(<ReasonPrompt {...defaultProps} />);
+
+    expect(screen.getByRole("button", { name: /blocking/i })).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: /urgent/i })).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: /context switch/i })).toBeInTheDocument();
+    expect(screen.getByRole("button", { name: /energy/i })).toBeInTheDocument();
+  });
+
+  it("shows different titles for different actions", () => {
+    const { rerender } = render(
+      <ReasonPrompt {...defaultProps} action="defer" itemTitle="Issue #42" />
+    );
+    expect(screen.getByText(/Deferring.*Issue #42/i)).toBeInTheDocument();
+
+    rerender(
+      <ReasonPrompt {...defaultProps} action="skip" itemTitle="MR !100" />
+    );
+    expect(screen.getByText(/Skipping.*MR !100/i)).toBeInTheDocument();
+  });
+});