fix(#274): Add input validation to prevent command injection in git operations

Implemented strict whitelist-based validation for git branch names and
repository URLs to prevent command injection vulnerabilities in worktree
operations.

Security fixes:
- Created git-validation.util.ts with whitelist validation functions
- Added custom DTO validators for branch names and repository URLs
- Applied defense-in-depth validation in WorktreeManagerService
- Comprehensive test coverage (31 tests) for all validation scenarios

Validation rules:
- Branch names: alphanumeric + hyphens + underscores + slashes + dots only
- Repository URLs: https://, http://, ssh://, git:// protocols only
- Blocks: option injection (--), command substitution ($(), ``), shell operators
- Prevents: SSRF attacks (localhost, internal networks), credential injection

Defense layers:
1. DTO validation (first line of defense at API boundary)
2. Service-level validation (defense-in-depth before git operations)

Fixes #274

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/orchestrator/src/git/worktree-manager.service.ts

@@ -3,6 +3,7 @@ import { simpleGit, SimpleGit } from "simple-git";
 import * as path from "path";
 import { GitOperationsService } from "./git-operations.service";
 import { WorktreeInfo, WorktreeError } from "./types";
+import { validateBranchName } from "./git-validation.util";
 
 /**
  * Result of worktree cleanup operation
@@ -70,6 +71,10 @@ export class WorktreeManagerService {
       throw new Error("taskId is required");
     }
 
+    // Validate baseBranch to prevent command injection
+    // This is defense-in-depth - DTO validation should catch this first
+    validateBranchName(baseBranch);
+
     const worktreePath = this.getWorktreePath(repoPath, agentId, taskId);
     const branchName = this.getBranchName(agentId, taskId);
 
@@ -79,6 +84,7 @@ export class WorktreeManagerService {
       const git = this.getGit(repoPath);
 
       // Create worktree with new branch
+      // baseBranch is validated above to prevent command injection
       await git.raw(["worktree", "add", worktreePath, "-b", branchName, baseBranch]);
 
       this.logger.log(`Successfully created worktree at ${worktreePath}`);