feat: Add pmg setup doctor command (#290)

* feat: add doctor check runner core types and logic

* feat: add doctor checks for config, binary, directory, and aliases

* feat: add doctor checks for sandbox and security features

* feat: add protection verification check using test malicious packages

* feat: add summarized package manager availability check

* feat: add pmg setup doctor command with compact output

* feat: add PATH shim verification to doctor command

* fix: improve doctor command UX and alias detection

- Capitalize all check messages for consistent output
- Dim passing checks, color warn/fail for visual clarity
- Silence empty Cobra error output on doctor failure
- Remove redundant pmg binary check (self-evident)
- Fix alias IsInstalled to skip commented-out source lines
- Improve protection failure message

* refactor: remove package manager availability check from doctor

* fix: handle os.RemoveAll error in doctor protection check

* refactor: use table layout for setup doctor, extract shared table renderer

Move renderTable, truncate, and visibleWidth helpers from cmd/sandbox
to internal/ui so both sandbox and setup doctor share them. Rewrite
setup doctor output to use the same table structure as sandbox doctor.
Fix VisibleWidth to count runes instead of bytes for correct alignment
with multi-byte UTF-8 characters.

* docs: add pmg setup doctor to README, remove manual verification step

* refactor: use constants for check names, rename and inline doctor helpers

Address PR review comments: extract check name constants, rename
CheckConfigFile to CheckFileExists and CheckDirectoryWritable to
CheckDirectoryExists for reusability, inline trivial wrappers
(CheckSandbox, CheckSecurityFeature, CheckProxyMode), and add
fix hints for all checks with correct config keys.

* refactor: inline simple doctor checks into command layer

* fix: skip protection check when aliases and shims are inactive

Protection checks now fail immediately when shell aliases and shims
are both inactive, instead of falsely passing by running through the
pmg binary directly. Also clean up summary messages to remove
redundant fix hints and truncated paths.

cmd/setup/setup.go

@@ -27,6 +27,7 @@ func NewSetupCommand() *cobra.Command {
 	setupCmd.AddCommand(NewInstallCommand())
 	setupCmd.AddCommand(NewRemoveCommand())
 	setupCmd.AddCommand(NewInfoCommand())
+	setupCmd.AddCommand(NewDoctorCommand())
 
 	return setupCmd
 }