feat: refactor plugin architecture, enhance linting, CI & tooling

- Major refactor of core Fish functions for modularity, caching, and error handling
- Improved `.editorconfig` and Makefile for stricter formatting and linting standards
- Expanded linting support: added EditorConfig checks, auto-install for missing tools, and Makefile targets
- Enhanced CI workflow with clearer permissions and job steps in GitHub Actions
- Updated documentation in `README.md` and `CLAUDE.md` to reflect new features, advanced developer tools, and contribution guidelines
- Improved Node.js version manager detection, switching, and installation logic
- Added/updated utility functions for configuration, silent mode, notifications, and version extraction
- Various bug fixes, code quality improvements, and expanded test coverage

tests/unit/test_auto_use_helpers.fish

@@ -0,0 +1,134 @@
+#!/usr/bin/env fish
+# Unit tests for nvm_auto_use helper functions
+
+source tests/test_runner.fish
+
+function test_select_manager
+    echo "Testing _nvm_auto_use_select_manager..."
+
+    # Mock nvm_compat_detect to return a list
+    function nvm_compat_detect
+        echo "nvm fnm volta"
+    end
+
+    set -e _nvm_auto_use_preferred_manager
+    set -l manager (_nvm_auto_use_select_manager)
+    assert_equals "$manager" nvm "Default manager selection returns first available"
+
+    set -g _nvm_auto_use_preferred_manager volta
+    set manager (_nvm_auto_use_select_manager)
+    assert_equals "$manager" volta "Preferred manager selection works"
+
+    set -e _nvm_auto_use_preferred_manager
+    functions -e nvm_compat_detect
+end
+
+function test_should_debounce
+    echo "Testing _nvm_auto_use_should_debounce..."
+
+    set -e _nvm_auto_use_last_change
+    set -g _nvm_auto_use_debounce_ms 1000
+
+    # First call should set last_change and return 1 (not debounced)
+    set result (_nvm_auto_use_should_debounce)
+    assert_equals "$result" "" "First call not debounced"
+
+    # Second call within debounce period should return 0 (debounced)
+    set result (_nvm_auto_use_should_debounce)
+    assert_equals "$result" "" "Second call debounced"
+
+    set -e _nvm_auto_use_last_change
+    set -e _nvm_auto_use_debounce_ms
+end
+
+function test_is_excluded_dir
+    echo "Testing _nvm_auto_use_is_excluded_dir..."
+
+    set -g _nvm_auto_use_excluded_dirs testdir
+    set -l orig_pwd (pwd)
+    cd /
+    mkdir -p testdir
+    cd testdir
+
+    set result (_nvm_auto_use_is_excluded_dir)
+    assert_equals "$result" "" "Excluded directory detected"
+
+    cd "$orig_pwd"
+    set -e _nvm_auto_use_excluded_dirs
+end
+
+function test_get_mtime
+    echo "Testing _nvm_auto_use_get_mtime..."
+
+    echo test >testfile
+    set mtime (_nvm_auto_use_get_mtime "testfile")
+    test -n "$mtime"
+    and echo "✅ mtime returned: $mtime"
+    or echo "❌ mtime not returned"
+
+    rm -f testfile
+end
+
+function test_is_cache_valid
+    echo "Testing _nvm_auto_use_is_cache_valid..."
+
+    set -g _nvm_auto_use_cached_file foo
+    set -g _nvm_auto_use_cached_mtime 123
+    set result (_nvm_auto_use_is_cache_valid "foo" "123")
+    assert_equals "$result" "" "Cache valid returns 0"
+
+    set result (_nvm_auto_use_is_cache_valid "bar" "123")
+    assert_equals "$result" "" "Cache invalid returns 1"
+
+    set -e _nvm_auto_use_cached_file
+    set -e _nvm_auto_use_cached_mtime
+end
+
+function test_clear_cache
+    echo "Testing _nvm_auto_use_clear_cache..."
+
+    set -g _nvm_auto_use_cached_file foo
+    set -g _nvm_auto_use_cached_version bar
+    set -g _nvm_auto_use_cached_mtime baz
+    _nvm_auto_use_clear_cache
+    if not set -q _nvm_auto_use_cached_file
+        echo "✅ Cached file cleared"
+    else
+        echo "❌ Cached file not cleared"
+    end
+    if not set -q _nvm_auto_use_cached_version
+        echo "✅ Cached version cleared"
+    else
+        echo "❌ Cached version not cleared"
+    end
+    if not set -q _nvm_auto_use_cached_mtime
+        echo "✅ Cached mtime cleared"
+    else
+        echo "❌ Cached mtime not cleared"
+    end
+end
+
+function main
+    setup_test_env
+
+    set -l failed 0
+
+    test_select_manager; or set failed (math "$failed + 1")
+    test_should_debounce; or set failed (math "$failed + 1")
+    test_is_excluded_dir; or set failed (math "$failed + 1")
+    test_get_mtime; or set failed (math "$failed + 1")
+    test_is_cache_valid; or set failed (math "$failed + 1")
+    test_clear_cache; or set failed (math "$failed + 1")
+
+    cleanup_test_env
+
+    if test $failed -eq 0
+        echo "🎉 All nvm_auto_use helper tests passed!"
+        return 0
+    else
+        echo "💥 $failed helper test(s) failed"
+        return 1
+    end
+end
+
+main