feat: add gitignore option to exclude ignored files from sources/generates

When `gitignore: true` is set at the Taskfile or task level, files
matching .gitignore rules are automatically excluded from sources and
generates glob resolution. This prevents rebuilds triggered by changes
to files that are in .gitignore (build artifacts, generated files, etc.).

Uses go-git to load .gitignore patterns including nested .gitignore
files, .git/info/exclude, and global gitignore configuration.

taskfile/ast/task.go

@@ -38,6 +38,7 @@ type Task struct {
 	Method        string
 	Prefix        string `hash:"ignore"`
 	IgnoreError   bool
+	Gitignore     *bool
 	Run           string
 	Platforms     []*Platform
 	If            string
@@ -75,6 +76,12 @@ func (t *Task) IsSilent() bool {
 	return t.Silent != nil && *t.Silent
 }
 
+// IsGitignore returns true if the task has gitignore filtering explicitly enabled.
+// Returns false if Gitignore is nil (not set) or explicitly set to false.
+func (t *Task) IsGitignore() bool {
+	return t.Gitignore != nil && *t.Gitignore
+}
+
 // WildcardMatch will check if the given string matches the name of the Task and returns any wildcard values.
 func (t *Task) WildcardMatch(name string) (bool, []string) {
 	names := append([]string{t.Task}, t.Aliases...)
@@ -150,6 +157,7 @@ func (t *Task) UnmarshalYAML(node *yaml.Node) error {
 			Method        string
 			Prefix        string
 			IgnoreError   bool `yaml:"ignore_error"`
+			Gitignore     *bool `yaml:"gitignore,omitempty"`
 			Run           string
 			Platforms     []*Platform
 			If            string
@@ -190,6 +198,7 @@ func (t *Task) UnmarshalYAML(node *yaml.Node) error {
 		t.Method = task.Method
 		t.Prefix = task.Prefix
 		t.IgnoreError = task.IgnoreError
+		t.Gitignore = deepcopy.Scalar(task.Gitignore)
 		t.Run = task.Run
 		t.Platforms = task.Platforms
 		t.If = task.If
@@ -233,6 +242,7 @@ func (t *Task) DeepCopy() *Task {
 		Method:               t.Method,
 		Prefix:               t.Prefix,
 		IgnoreError:          t.IgnoreError,
+		Gitignore:            deepcopy.Scalar(t.Gitignore),
 		Run:                  t.Run,
 		IncludeVars:          t.IncludeVars.DeepCopy(),
 		IncludedTaskfileVars: t.IncludedTaskfileVars.DeepCopy(),