Add 5 test files for game module targeting dev

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Summary

Added 5 new test files with comprehensive unit tests for the game module targeting dev:

Tests Added

src/game/input_mapper_tests.zig (32 tests)

• InputBinding.getName() for all key types and mouse buttons
• InputBinding.eql() bidirectional key/key_alt equality
• ActionBinding.init() and initWithAlt()
• DEFAULT_BINDINGS verification for all GameAction values
• InputMapper.setBinding(), setAlternateBinding(), resetToDefaults(), resetActionToDefault()
• InputMapper.interface() vtable creation

src/game/settings/data_tests.zig (18 tests)

• Settings.getShadowResolution() for all quality levels and invalid values
• Settings.getResolutionIndex() and setResolutionByIndex() for all resolutions
• SHADOW_QUALITIES array validation
• RESOLUTIONS array ordering and common resolutions
• ShadowDebugChannel enum values
• resolveShadowDebugChannel() priority ordering (seam_diagnostics > caster_coverage > cascade_index > shadow_factor > off)

src/game/settings/presets_tests.zig (5 tests)

• getPresetName() for valid and out-of-bounds indices
• getIndex() returns len (Custom) for non-matching settings
• apply() ignores out-of-bounds indices
• apply() correctly sets all fields from preset

src/game/settings/apply_tests.zig (3 tests)

• applyToRenderSettings() calls all 8 relevant setter methods
• False values propagate correctly
• Edge case values (min, max) handled correctly

src/game/settings/persistence_tests.zig (9 tests)

• setTexturePack() early return when setting same value
• setTexturePack() changes value when different
• setTexturePack() multiple changes with proper memory management
• setEnvironmentMap() same/different value handling
• deinit() handles both static "default" and allocated strings
• texture_pack and environment_map are independent

Verification

• nix develop --command zig fmt src/ passes
• nix develop --command zig build test passes (all 696 tests)
• No non-test source files were modified

Triggered by scheduled workflow

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