Fix cargo availability in dev-shell environment

- Add cargo to PATH in dev-shell service
- Add target-cache volume for Rust build caching
- Use login shell to properly source cargo environment
- Keeps existing build infrastructure and caching strategy

build/docker-compose.yml

@@ -72,9 +72,12 @@ services:
   dev-shell:
     extends: builder
     container_name: zero-os-alpine-dev-shell
-    command: /bin/sh
+    command: /bin/sh -l
     stdin_open: true
     tty: true
+    environment:
+      - PATH=/root/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+      - CARGO_TARGET_DIR=/build/target-cache
     volumes:
       - ../configs:/build/configs
       - ../scripts:/build/scripts
@@ -83,6 +86,7 @@ services:
       - build-cache:/build/cache
       - source-cache:/build/source
       - kernel-cache:/build/kernel
+      - target-cache:/build/target-cache
       - ../configs/zinit:/mnt/zinit:ro
 
   # Test build with minimal caching (for testing clean builds)
@@ -125,6 +129,7 @@ volumes:
   build-cache:
   source-cache:
   kernel-cache:
+  target-cache:
   
   # Legacy volumes (for fallback)
   github-cache: