fix: harden Docker environment so tests pass inside container

- Add procps to runtime stage so `ps` is available for process management
- Remove noexec from /tmp and /home/storkit tmpfs mounts so test scripts
  can be executed from tempdir
- Update coder agent system_prompt to run clippy --all-targets --all-features
  matching what the server acceptance gate actually runs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker/Dockerfile

@@ -67,6 +67,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
         build-essential \
         pkg-config \
         libssl-dev \
+        # procps provides ps, needed by tests and process management
+        procps \
     && rm -rf /var/lib/apt/lists/*
 
 # Node.js in runtime

docker/docker-compose.yml

@@ -71,8 +71,8 @@ services:
     # tmpfs paths are writable.
     read_only: true
     tmpfs:
-      - /tmp:size=512M
-      - /home/storkit:size=512M,uid=999,gid=999
+      - /tmp:size=512M,exec
+      - /home/storkit:size=512M,uid=999,gid=999,exec
 
     # Drop all Linux capabilities, then add back only what's needed.
     # SETUID/SETGID needed by Claude Code's PTY allocation (openpty).