Add support for yarn package manager (#72)

* Add support for yarn package manager

- Added yarn command handler in cmd/npm/yarn.go
- Added DefaultYarnPackageManagerConfig() in packagemanager/npm.go
- Added yarn dev flag support (--dev/-D) in ParseCommand()
- Added yarn analytics tracking in internal/analytics/event.go
- Registered yarn command in main.go
- Added yarn to alias setup in internal/alias/alias.go
- Added comprehensive test suite in packagemanager/yarn_test.go
- All tests passing (12 yarn tests + existing tests)

Resolves #30

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

* docs: update README with yarn package manager support

Updated documentation to reflect yarn support addition:
- Changed yarn status from '🚧 Planned' to '✅ Active' in package managers table
- Added 'pmg yarn add <package>' command example
- Added 'yarn add <package-name>' to command list
- Added 'yarn install # Uses yarn.lock' to lockfile examples

This documentation update corresponds to the yarn implementation in the previous commit.

Related to #30

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

* fix: address review feedback for yarn support

- Add support for bare 'yarn' command as manifest install
- Validate yarn install does not accept package names
- Add YarnExtractor for yarn.lock file support

Changes:
- packagemanager/npm.go: Added bare yarn command handling and validation
- packagemanager/yarn_test.go: Added test for bare yarn command
- extractor/ecosystems.go: Added Yarn PackageManagerName and extractor
- extractor/npm.go: Added YarnExtractor implementation
- go.mod, go.sum: Updated dependencies

Addresses review feedback from @Sahilb315
- Bare yarn command now triggers manifest install per docs
- yarn install <package> is now properly rejected
- yarn.lock extraction support added

Related to #30

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

* chore: tidy go.mod and go.sum to remove unused dependencies

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

* fix: add yarn.lock extractor mapping

- Add yarn.lock case in getExtractorForFile switch
- Import yarnlock extractor from osv-scalibr
- Enables lockfile parsing for manifest-based installations

Tested both package-based and manifest-based installations successfully.

Addresses review feedback from @Sahilb315

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

* test: add validation test for yarn install with package name

- Add test case to verify 'yarn install <package>' is rejected
- Ensures invalid syntax returns no install targets
- Confirms IsManifestInstall is false for invalid commands

Addresses review feedback from @Sahilb315

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

---------

Signed-off-by: shrvansudhakara <shrvansudhakara@gmail.com>

internal/analytics/event.go

@@ -5,6 +5,7 @@ const (
 	eventCommandNpm    = "pmg_command_npm"
 	eventCommandBun    = "pmg_command_bun"
 	eventCommandPnpm   = "pmg_command_pnpm"
+	eventCommandYarn   = "pmg_command_yarn"
 	eventCommandPip    = "pmg_command_pip"
 	eventCommandUv     = "pmg_command_uv"
 	eventCommandPoetry = "pmg_command_poetry"
@@ -30,6 +31,10 @@ func TrackCommandPnpm() {
 	TrackEvent(eventCommandPnpm)
 }
 
+func TrackCommandYarn() {
+	TrackEvent(eventCommandYarn)
+}
+
 func TrackCommandPip() {
 	TrackEvent(eventCommandPip)
 }