feat: simplify to two modes (tag and agent) for v1.0

BREAKING CHANGES:
- Remove review mode entirely - now handled via slash commands in agent mode
- Remove all deprecated backward compatibility fields (mode, anthropic_model, override_prompt, direct_prompt)
- Simplify mode detection: prompt overrides everything, then @claude mentions trigger tag mode, default is agent mode
- Remove slash command resolution from GitHub Action - Claude Code handles natively
- Remove variable substitution - prompts passed through as-is

Architecture changes:
- Only two modes now: tag (for @claude mentions) and agent (everything else)
- Agent mode is the default for all events including PRs
- Users configure behavior via prompts/slash commands (e.g. /review)
- GitHub Action is now a thin wrapper that passes prompts to Claude Code
- Mode names changed: 'experimental-review' → removed entirely

This aligns with the philosophy that the GitHub Action should do minimal work and delegate to Claude Code for all intelligent behavior.

test/modes/registry.test.ts

@@ -1,7 +1,7 @@
 import { describe, test, expect } from "bun:test";
 import { getMode, isValidMode } from "../../src/modes/registry";
 import { agentMode } from "../../src/modes/agent";
-import { reviewMode } from "../../src/modes/review";
+import { tagMode } from "../../src/modes/tag";
 import { createMockContext, createMockAutomationContext } from "../mockContext";
 
 describe("Mode Registry", () => {
@@ -36,11 +36,7 @@ describe("Mode Registry", () => {
     expect(mode.name).toBe("agent");
   });
 
-  test("getMode can use explicit mode override for review", () => {
-    const mode = getMode(mockContext, "review");
-    expect(mode).toBe(reviewMode);
-    expect(mode.name).toBe("experimental-review");
-  });
+  // Removed test - explicit mode override no longer supported in v1.0
 
   test("getMode auto-detects agent for workflow_dispatch", () => {
     const mode = getMode(mockWorkflowDispatchContext);
@@ -54,37 +50,64 @@ describe("Mode Registry", () => {
     expect(mode.name).toBe("agent");
   });
 
-  test("getMode supports legacy experimental-review mode name", () => {
-    const mode = getMode(mockContext, "experimental-review");
-    expect(mode).toBe(reviewMode);
-    expect(mode.name).toBe("experimental-review");
-  });
+  // Removed test - legacy mode names no longer supported in v1.0
 
-  test("getMode auto-detects review mode for PR opened", () => {
+  test("getMode auto-detects agent mode for PR opened", () => {
     const prContext = createMockContext({
       eventName: "pull_request",
       payload: { action: "opened" } as any,
       isPR: true,
     });
     const mode = getMode(prContext);
-    expect(mode).toBe(reviewMode);
-    expect(mode.name).toBe("experimental-review");
-  });
-
-  test("getMode falls back to auto-detection for invalid mode override", () => {
-    const mode = getMode(mockContext, "invalid");
-    // Should fall back to auto-detection, which returns agent for issue_comment without trigger
     expect(mode).toBe(agentMode);
     expect(mode.name).toBe("agent");
   });
 
+  test("getMode uses agent mode when prompt is provided, even with @claude mention", () => {
+    const contextWithPrompt = createMockContext({
+      eventName: "issue_comment",
+      payload: {
+        action: "created",
+        comment: {
+          body: "@claude please help",
+        },
+      } as any,
+      inputs: {
+        prompt: "/review",
+      } as any,
+    });
+    const mode = getMode(contextWithPrompt);
+    expect(mode).toBe(agentMode);
+    expect(mode.name).toBe("agent");
+  });
+
+  test("getMode uses tag mode for @claude mention without prompt", () => {
+    const contextWithMention = createMockContext({
+      eventName: "issue_comment",
+      payload: {
+        action: "created",
+        comment: {
+          body: "@claude please help",
+        },
+      } as any,
+      inputs: {
+        triggerPhrase: "@claude",
+      } as any,
+    });
+    const mode = getMode(contextWithMention);
+    expect(mode).toBe(tagMode);
+    expect(mode.name).toBe("tag");
+  });
+
+  // Removed test - explicit mode override no longer supported in v1.0
+
   test("isValidMode returns true for all valid modes", () => {
     expect(isValidMode("tag")).toBe(true);
     expect(isValidMode("agent")).toBe(true);
-    expect(isValidMode("experimental-review")).toBe(true);
   });
 
   test("isValidMode returns false for invalid mode", () => {
     expect(isValidMode("invalid")).toBe(false);
+    expect(isValidMode("review")).toBe(false);
   });
 });