feat: implement Claude Code GitHub Action v1.0 with auto-detection and slash commands

Major features:
- Mode auto-detection based on GitHub event type
- Unified prompt field replacing override_prompt and direct_prompt
- Slash command system with pre-built commands
- Full backward compatibility with v0.x

Key changes:
- Add mode detector for automatic mode selection
- Implement slash command loader with YAML frontmatter support
- Update action.yml with new prompt input
- Create pre-built slash commands for common tasks
- Update all tests for v1.0 compatibility

Breaking changes (with compatibility):
- Mode input now optional (auto-detected)
- override_prompt deprecated (use prompt)
- direct_prompt deprecated (use prompt)

src/github/context.ts

@@ -35,7 +35,6 @@ export type ScheduleEvent = {
   };
 };
 import type { ModeName } from "../modes/types";
-import { DEFAULT_MODE, isValidMode } from "../modes/registry";
 
 // Event name constants for better maintainability
 const ENTITY_EVENT_NAMES = [
@@ -63,15 +62,16 @@ type BaseContext = {
   };
   actor: string;
   inputs: {
-    mode: ModeName;
+    mode?: ModeName; // Optional for v1.0 backward compatibility
+    prompt: string; // New unified prompt field
     triggerPhrase: string;
     assigneeTrigger: string;
     labelTrigger: string;
     allowedTools: string[];
     disallowedTools: string[];
     customInstructions: string;
-    directPrompt: string;
-    overridePrompt: string;
+    directPrompt: string; // Deprecated, kept for compatibility
+    overridePrompt: string; // Deprecated, kept for compatibility
     baseBranch?: string;
     branchPrefix: string;
     useStickyComment: boolean;
@@ -105,10 +105,8 @@ export type GitHubContext = ParsedGitHubContext | AutomationContext;
 export function parseGitHubContext(): GitHubContext {
   const context = github.context;
 
-  const modeInput = process.env.MODE ?? DEFAULT_MODE;
-  if (!isValidMode(modeInput)) {
-    throw new Error(`Invalid mode: ${modeInput}.`);
-  }
+  // Mode is optional in v1.0 (auto-detected)
+  const modeInput = process.env.MODE ? process.env.MODE as ModeName : undefined;
 
   const commonFields = {
     runId: process.env.GITHUB_RUN_ID!,
@@ -120,15 +118,19 @@ export function parseGitHubContext(): GitHubContext {
     },
     actor: context.actor,
     inputs: {
-      mode: modeInput as ModeName,
+      mode: modeInput,
+      // v1.0: Unified prompt field with fallback to legacy fields
+      prompt: process.env.PROMPT || 
+              process.env.OVERRIDE_PROMPT || 
+              process.env.DIRECT_PROMPT || "",
       triggerPhrase: process.env.TRIGGER_PHRASE ?? "@claude",
       assigneeTrigger: process.env.ASSIGNEE_TRIGGER ?? "",
       labelTrigger: process.env.LABEL_TRIGGER ?? "",
       allowedTools: parseMultilineInput(process.env.ALLOWED_TOOLS ?? ""),
       disallowedTools: parseMultilineInput(process.env.DISALLOWED_TOOLS ?? ""),
       customInstructions: process.env.CUSTOM_INSTRUCTIONS ?? "",
-      directPrompt: process.env.DIRECT_PROMPT ?? "",
-      overridePrompt: process.env.OVERRIDE_PROMPT ?? "",
+      directPrompt: process.env.DIRECT_PROMPT ?? "", // Deprecated
+      overridePrompt: process.env.OVERRIDE_PROMPT ?? "", // Deprecated
       baseBranch: process.env.BASE_BRANCH,
       branchPrefix: process.env.BRANCH_PREFIX ?? "claude/",
       useStickyComment: process.env.USE_STICKY_COMMENT === "true",