refactor(test): migrate lint tests to use reusable fixtures

Migrates 10 test functions in lint_test.go to use testdata fixtures
instead of inline file creation, following the pattern established
in image_extraction_test.go.

Changes:
- Add helper functions: getTestDataPath, copyFixtureToTemp
- Create testdata/lint/ with 39 fixture files across 8 scenarios
- Migrate tests: TestLint_VerboseFlag, TestLint_ChartValidationError,
  TestLint_AutodiscoveryWithMixedManifests, and 7 others
- Reduce test file: 2,355 → 1,888 lines (20% reduction)
- Reduce os.WriteFile calls: 74 → 42 (43% reduction)

Fixtures created:
- simple-chart/ - Basic chart for simple tests
- multi-chart-project/ - Multiple charts scenario
- chart-missing-helmchart/ - Validation error tests
- orphaned-helmchart/ - Validation warning tests
- mixed-manifests-autodiscovery/ - Mixed resource types
- mixed-manifests-yaml-yml/ - Mixed file extensions (.yaml/.yml)
- hidden-dirs-test/ - Hidden directory testing (.github)
- configs/ - 6 reusable config templates

Remaining inline tests use dynamic paths, test error scenarios,
or are minimal configs where fixtures would add overhead.

All tests pass.

Author: Bishibop

cli/cmd/lint_test.go

@@ -0,0 +1,10 @@
+charts:
+  - path: chart
+manifests:
+  - manifests/*.yaml
+repl-lint:
+  linters:
+    helm:
+      disabled: true
+    preflight:
+      disabled: true

testdata/lint/chart-missing-helmchart/.replicated

@@ -0,0 +1,4 @@
+apiVersion: v2
+name: test-app
+version: 1.0.0
+description: Test chart without matching HelmChart manifest

testdata/lint/chart-missing-helmchart/chart/Chart.yaml

@@ -0,0 +1 @@
+# Empty manifests directory - no HelmChart manifest

testdata/lint/chart-missing-helmchart/manifests/.gitkeep

@@ -0,0 +1,6 @@
+repl-lint:
+  version: 1
+  linters:
+    helm: {}
+    preflight: {}
+    support-bundle: {}

testdata/lint/configs/all-linters-enabled.yaml

@@ -0,0 +1,5 @@
+repl-lint:
+  linters:
+    helm: {}
+    preflight:
+      disabled: true

testdata/lint/configs/basic-helm-lint.yaml

@@ -0,0 +1,8 @@
+charts: []
+manifests: []
+preflights: []
+repl-lint:
+  linters:
+    helm: {}
+    preflight:
+      disabled: true

testdata/lint/configs/empty-config.yaml

@@ -0,0 +1,9 @@
+repl-lint:
+  tools:
+    helm: "latest"
+    preflight: "latest"
+    support-bundle: "latest"
+  linters:
+    helm: {}
+    preflight:
+      disabled: true

testdata/lint/configs/helm-with-latest.yaml

@@ -0,0 +1,9 @@
+repl-lint:
+  tools:
+    helm: "3.14.4"
+    preflight: "0.123.9"
+    support-bundle: "0.123.9"
+  linters:
+    helm: {}
+    preflight:
+      disabled: true

testdata/lint/configs/helm-with-versions.yaml

@@ -0,0 +1,6 @@
+manifests:
+  - manifests/*.yaml
+repl-lint:
+  linters:
+    helm: {}
+    preflight: {}