Fix keyboard shortcuts broken by NumLock/CapsLock

[christianparpart]

Summary

Fixes #1901.

• Strip lock modifiers (NumLock, CapsLock) from incoming key events before matching against configured key bindings in config::apply()
• Promote LockModifiers constant from InputGenerator.cpp (file-local) to InputGenerator.h (shared) so it can be reused across binding matching and legacy input generation
• Add 4 new test cases verifying lock-modifier stripping behavior

Root cause

The Modifier enum includes NumLock=128 and CapsLock=64 as first-class bit flags. Key binding matching in config::apply() used exact equality (mapping.modifiers == modifiers), so Shift|Control|NumLock ≠ Shift|Control and the binding would silently fail. The VT input generator already stripped lock modifiers — this fix applies the same treatment to the shortcut matching path.

Risk assessment

Low risk. The change is a single bitwise AND-NOT on a uint8_t before comparison. When no lock keys are active, modifiers.without(LockModifiers) is a no-op. No behavior change for users without lock keys active.

Test plan

• All existing tests pass (ctest --preset=clang-debug — 5/5)
• New tests: InputBinding.match_with_NumLock_stripped, InputBinding.match_with_CapsLock_stripped, InputBinding.match_with_NumLock_and_CapsLock_stripped, InputBinding.match_still_requires_real_modifiers
• Manual: With NumLock on, verify Ctrl+Shift+N triggers NewTerminal

[Copilot]

Pull request overview

This PR fixes issue #1901 where keyboard shortcuts could fail to match when NumLock/CapsLock were active by stripping lock modifiers from incoming modifier masks before comparing against configured input bindings.

Changes:

• Promote LockModifiers to InputGenerator.h for shared reuse.
• Strip LockModifiers in contour::config::apply() before matching bindings.
• Add new unit tests intended to cover lock-modifier stripping behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/vtbackend/InputGenerator.h	Exposes LockModifiers as a shared constexpr for reuse across components.
src/vtbackend/InputGenerator.cpp	Removes file-local LockModifiers and relies on the shared header constant.
src/contour/Config.h	Strips lock modifiers before comparing mapping.modifiers against event modifiers in apply().
src/vtbackend/InputGenerator_test.cpp	Adds new tests around lock-modifier behavior (currently not directly exercising config::apply()).

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