chore(branchlet): Remove docs pip install from postCreateCmd (#11883)

### Changes 🏗️

- Removed `cd docs && pip install -r requirements.txt` from
`postCreateCmd` in `.branchlet.json`
- Docs dependencies will no longer be auto-installed during branchlet
worktree creation

### Rationale

The docs setup step was adding unnecessary overhead to the worktree
creation process. Developers who need to work on documentation can
manually install the docs requirements when needed.

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
- [x] Verified branchlet worktree creation still works without the docs
pip install step

#### For configuration changes:

- [x] `.env.default` is updated or already compatible with my changes
- [x] `docker-compose.yml` is updated or already compatible with my
changes
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

.branchlet.json

@@ -29,8 +29,7 @@
   "postCreateCmd": [
     "cd autogpt_platform/autogpt_libs && poetry install",
     "cd autogpt_platform/backend && poetry install && poetry run prisma generate",
-    "cd autogpt_platform/frontend && pnpm install",
-    "cd docs && pip install -r requirements.txt"
+    "cd autogpt_platform/frontend && pnpm install"
   ],
   "terminalCommand": "code .",
   "deleteBranchWithWorktree": false