fix: use path.join for cross-platform compatibility in Codex FILE_PATHS

Fixes #132

The FILE_PATHS constant was using hardcoded forward slashes, which caused
path.basename() to fail on Windows. On Windows, path.basename() expects
backslashes as path separators, so it would return the entire string
instead of just the filename.

This broke Codex detection on Windows during init/update because the
resolveAbsolutePath() method would construct incorrect paths, causing
file existence checks to fail.

Changed FILE_PATHS to use path.join() which automatically uses the
correct platform-specific path separators (backslashes on Windows,
forward slashes on Unix).

src/core/configurators/slash/codex.ts

@@ -5,11 +5,10 @@ import { SlashCommandId, TemplateManager } from "../../templates/index.js";
 import { FileSystemUtils } from "../../../utils/file-system.js";
 import { OPENSPEC_MARKERS } from "../../config.js";
 
-// Use POSIX-style paths for consistent logging across platforms.
 const FILE_PATHS: Record<SlashCommandId, string> = {
-  proposal: ".codex/prompts/openspec-proposal.md",
-  apply: ".codex/prompts/openspec-apply.md",
-  archive: ".codex/prompts/openspec-archive.md",
+  proposal: path.join(".codex", "prompts", "openspec-proposal.md"),
+  apply: path.join(".codex", "prompts", "openspec-apply.md"),
+  archive: path.join(".codex", "prompts", "openspec-archive.md"),
 };
 
 export class CodexSlashCommandConfigurator extends SlashCommandConfigurator {

src/core/update.ts

@@ -106,9 +106,9 @@ export class UpdateCommand {
     }
 
     if (updatedSlashFiles.length > 0) {
-      // Normalize to forward slashes for cross-platform log consistency
-      const normalized = updatedSlashFiles.map((p) => p.replace(/\\/g, '/'));
-      summaryParts.push(`Updated slash commands: ${normalized.join(', ')}`);
+      summaryParts.push(
+        `Updated slash commands: ${updatedSlashFiles.join(', ')}`
+      );
     }
 
     const failedItems = [