feat(config): add branch prefix configuration (#197)

src/github/context.ts

@@ -35,6 +35,7 @@ export type ParsedGitHubContext = {
     customInstructions: string;
     directPrompt: string;
     baseBranch?: string;
+    branchPrefix: string;
   };
 };
 
@@ -60,6 +61,7 @@ export function parseGitHubContext(): ParsedGitHubContext {
       customInstructions: process.env.CUSTOM_INSTRUCTIONS ?? "",
       directPrompt: process.env.DIRECT_PROMPT ?? "",
       baseBranch: process.env.BASE_BRANCH,
+      branchPrefix: process.env.BRANCH_PREFIX ?? "claude/",
     },
   };