fix: project sleds need claude CLI + extensions.worktreeConfig

Two issues that surfaced when story 1 ran in the adopted huskies-server
sled:

1. Dockerfile.base: the base image had no nodejs / claude CLI, so every
   coder agent spawn in an adopted project sled failed with
   `Unable to spawn claude: No viable candidates found in PATH`.  Install
   nodejs + @anthropic-ai/claude-code in the base image so every sled
   built from it can spawn agents out of the box.

2. worktree/create.rs::install_pre_commit_hook: `git config --worktree`
   requires `extensions.worktreeConfig = true` to be set on the repo
   config; without it, every worktree creation logged a noisy
   `Pre-commit hook install failed` warning.  Enable the extension
   idempotently before the per-worktree hooks-path set so the hook
   install succeeds cleanly.

After this, rebuild huskies-project-base and recreate any adopted
project containers to pick up the CLI.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docker/Dockerfile.base

@@ -27,6 +27,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         procps \
         openssh-server \
         sudo \
+        nodejs \
+        npm \
+    && npm install -g @anthropic-ai/claude-code \
     && rm -rf /var/lib/apt/lists/*
 
 # Copy the huskies binary and entrypoint from the main image.