cmds.pkg.CmdVerify: Add command

Add the "packages verify" command: it runs Distro.verify() with the app's
package filter and prints one line per flagged file.

Signed-off-by: Jan Lindemann <jan@janware.com>
Assisted-by: unsloth/Qwen3.8-27B-GGUF:Q4_K_M with pi.dev v1.2.0

test/integration/jw_pkg/help/test-expected.txt

@@ -66,6 +66,8 @@ Available subcommands of packages:
     reboot-required  Check whether the machine needs rebooting
     refresh          Refresh the distribution's notion of available packages
     select           Select packages by filter
+    verify           Verify the integrity of installed packages: report files
+                     modified or deleted outside of the package manager
 ============= Running: jw-pkg.py -t ../../../.. --log-level info packages delete --help
 usage: jw-pkg.py packages delete [-h] [names ...]
 
@@ -140,6 +142,14 @@ Select packages by filter
 positional arguments:
   filter      Package filter string
 
+options:
+  -h, --help  show this help message and exit
+============= Running: jw-pkg.py -t ../../../.. --log-level info packages verify --help
+usage: jw-pkg.py packages verify [-h]
+
+Verify the integrity of installed packages: report files modified or deleted
+outside of the package manager
+
 options:
   -h, --help  show this help message and exit
 ============= Running: jw-pkg.py -t ../../../.. --log-level info platform --help