feat(linter): context-scoped needs:/dependencies: cross-checks

When glint check runs in single-context mode (--branch, --tag, --source,
or --var), jobs that resolve to JobSkipped against that context are now
excluded from needs: and dependencies: cross-job checks (GL027-GL031).
This eliminates false-positive errors for jobs intentionally gated to
specific pipeline events (e.g. a deploy job with rules:if: CI_COMMIT_TAG
no longer triggers GL027 on branch pipelines).

linter.Lint now accepts a skipped map[string]bool (nil = check all jobs);
checkNeeds and checkDependencies skip jobs present in the map. Multi-context
mode (--context) passes nil, so all jobs are checked regardless of context.

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

internal/linter/needs_test.go

@@ -6,6 +6,31 @@ import (
 	"git.k3nny.fr/glint/internal/model"
 )
 
+// TestCheckNeeds_SkippedJob verifies that a skipped job's needs: violations are suppressed.
+func TestCheckNeeds_SkippedJob(t *testing.T) {
+	p := &model.Pipeline{
+		Stages: []string{"build", "deploy"},
+		Jobs: map[string]model.Job{
+			"skipped-job": {
+				Name:   "skipped-job",
+				Stage:  "build",
+				Script: []any{"echo"},
+				Needs:  []any{"nonexistent-job"},
+			},
+		},
+	}
+	// Without skipping: should report unknown needs.
+	withoutSkip := checkNeeds(p, nil)
+	if len(withoutSkip) == 0 {
+		t.Fatal("expected GL027 without skipped set, got none")
+	}
+	// With job skipped: no findings.
+	withSkip := checkNeeds(p, map[string]bool{"skipped-job": true})
+	if len(withSkip) != 0 {
+		t.Errorf("expected no findings for skipped job, got %v", withSkip)
+	}
+}
+
 // TestCheckNeeds_StageOrder verifies that a job needing a job in a later stage
 // produces RuleNeedsStageOrder (line 64-76 in needs.go).
 func TestCheckNeeds_StageOrder(t *testing.T) {
@@ -25,7 +50,7 @@ func TestCheckNeeds_StageOrder(t *testing.T) {
 			},
 		},
 	}
-	findings := checkNeeds(p)
+	findings := checkNeeds(p, nil)
 	var gotStageOrder bool
 	for _, f := range findings {
 		if f.Rule == RuleNeedsStageOrder {