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.

src/modes/registry.ts

@@ -8,11 +8,10 @@
 import type { Mode, ModeName } from "./types";
 import { tagMode } from "./tag";
 import { agentMode } from "./agent";
-import { reviewMode } from "./review";
 import type { GitHubContext } from "../github/context";
 import { detectMode, type AutoDetectedMode } from "./detector";
 
-export const VALID_MODES = ["tag", "agent", "review"] as const;
+export const VALID_MODES = ["tag", "agent"] as const;
 
 /**
  * All available modes in v1.0
@@ -20,28 +19,19 @@ export const VALID_MODES = ["tag", "agent", "review"] as const;
 const modes = {
   tag: tagMode,
   agent: agentMode,
-  review: reviewMode,
 } as const satisfies Record<AutoDetectedMode, Mode>;
 
 /**
  * Automatically detects and retrieves the appropriate mode based on the GitHub context.
  * In v1.0, modes are auto-selected based on event type.
  * @param context The GitHub context
- * @param explicitMode Optional explicit mode override (for backward compatibility)
  * @returns The appropriate mode for the context
  */
-export function getMode(context: GitHubContext, explicitMode?: string): Mode {
-  let modeName: AutoDetectedMode;
-
-  if (explicitMode && isValidModeV1(explicitMode)) {
-    console.log(`Using explicit mode: ${explicitMode}`);
-    modeName = mapLegacyMode(explicitMode);
-  } else {
-    modeName = detectMode(context);
-    console.log(
-      `Auto-detected mode: ${modeName} for event: ${context.eventName}`,
-    );
-  }
+export function getMode(context: GitHubContext): Mode {
+  const modeName = detectMode(context);
+  console.log(
+    `Auto-detected mode: ${modeName} for event: ${context.eventName}`,
+  );
 
   const mode = modes[modeName];
   if (!mode) {
@@ -54,29 +44,11 @@ export function getMode(context: GitHubContext, explicitMode?: string): Mode {
 }
 
 /**
- * Maps legacy mode names to v1.0 mode names
- */
-function mapLegacyMode(name: string): AutoDetectedMode {
-  if (name === "experimental-review") {
-    return "review";
-  }
-  return name as AutoDetectedMode;
-}
-
-/**
- * Type guard to check if a string is a valid v1.0 mode name.
+ * Type guard to check if a string is a valid mode name.
  * @param name The string to check
  * @returns True if the name is a valid mode name
  */
-export function isValidModeV1(name: string): boolean {
-  const v1Modes = ["tag", "agent", "review", "experimental-review"];
-  return v1Modes.includes(name);
-}
-
-/**
- * Legacy type guard for backward compatibility
- * @deprecated Use auto-detection instead
- */
 export function isValidMode(name: string): name is ModeName {
-  return isValidModeV1(name);
+  const validModes = ["tag", "agent"];
+  return validModes.includes(name);
 }