feat: add linter with formatting rules, duplicate detection, sorting, and auto-fix

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/linter/linter.go

@@ -0,0 +1,60 @@
+package linter
+
+import (
+	"github.com/veggiemonk/awesome-docker/internal/parser"
+)
+
+// Result holds all lint issues found.
+type Result struct {
+	Issues   []Issue
+	Errors   int
+	Warnings int
+}
+
+// Lint checks an entire parsed document for issues.
+func Lint(doc parser.Document) Result {
+	var result Result
+
+	// Collect all entries for duplicate checking
+	allEntries := collectEntries(doc.Sections)
+	for _, issue := range CheckDuplicates(allEntries) {
+		addIssue(&result, issue)
+	}
+
+	// Check each section
+	lintSections(doc.Sections, &result)
+
+	return result
+}
+
+func lintSections(sections []parser.Section, result *Result) {
+	for _, s := range sections {
+		for _, e := range s.Entries {
+			for _, issue := range CheckEntry(e) {
+				addIssue(result, issue)
+			}
+		}
+		for _, issue := range CheckSorted(s.Entries) {
+			addIssue(result, issue)
+		}
+		lintSections(s.Children, result)
+	}
+}
+
+func collectEntries(sections []parser.Section) []parser.Entry {
+	var all []parser.Entry
+	for _, s := range sections {
+		all = append(all, s.Entries...)
+		all = append(all, collectEntries(s.Children)...)
+	}
+	return all
+}
+
+func addIssue(result *Result, issue Issue) {
+	result.Issues = append(result.Issues, issue)
+	if issue.Severity == SeverityError {
+		result.Errors++
+	} else {
+		result.Warnings++
+	}
+}