fix(macos): preserve Fn semantics for page navigation

[devsaddle]

Summary

Add macOS Fn/Globe support to custom shortcuts and reproduce the native navigation-key event representation. This makes synthesized page navigation match physical Fn+Up/Fn+Down instead of producing the shorter scroll behavior seen with flagged arrow-key events.

Changes

• openlogi-core
  • add KeyCombo::MOD_FN as modifier bit 0x10
  • render Fn before the standard macOS modifier symbols and render common navigation keys in generated shortcut labels
  • cover combined Fn modifier labels and TOML round trips
• openlogi-inject
  • map MOD_FN to CGEventFlagSecondaryFn on macOS
  • normalize Fn+Left/Right/Up/Down to Home/End/Page Up/Page Down virtual key codes while preserving CGEventFlagSecondaryFn
  • cover explicit Fn shortcuts and Page Up/Page Down compatibility behavior
• documentation and examples
  • document the modifier mask and Fn+arrow TOML configuration
  • include the Fn bit in the injection example help

Testing

• cargo fmt --all -- --check
• cargo test -p openlogi-core -p openlogi-inject --locked (99 core tests, 4 inject tests)
• cargo clippy -p openlogi-core -p openlogi-inject --all-targets --locked -- -D warnings
• cargo test --workspace --exclude openlogi-gui --locked
• cargo clippy --workspace --all-targets --locked -- -D warnings reached the GPUI macOS shader build and was blocked by the local Xcode installation missing the optional Metal Toolchain
• Hardware validated with an MX Master 2S: Page Up/Page Down in Safari and explicit Fn+Up/Fn+Down in Chrome both scroll a full page; Fn+Left/Fn+Right are covered by unit tests but were not runtime-tested on hardware

Related to #101.

[greptile-apps]

Greptile Summary

This PR adds macOS Fn/Globe modifier support to the custom-shortcut system. It introduces MOD_FN (bit 0x10) in openlogi-core, updates rendered_label to display fn first and recognize navigation key codes, and extracts a custom_shortcut_event helper in openlogi-inject that remaps MOD_FN + Arrow to the correct Home/End/Page Up/Page Down virtual key codes with CGEventFlagSecondaryFn, matching the events a physical Fn+arrow key press produces.

• MOD_FN bit added to KeyCombo, with label rendering, TOML round-trip, and modifier-ordering tests.
• custom_shortcut_event centralizes flag and key-code translation; Fn+Up/Down → Page Up/Down and Fn+Left/Right → Home/End are both mapped with SecondaryFn.
• Direct Page Up/Down shortcuts (no MOD_FN) auto-receive SecondaryFn; the analogous Home/End path is currently omitted from that condition.

Confidence Score: 5/5

Safe to merge — the core Fn+Arrow to Page Up/Page Down flow is well-tested and handles all four arrow directions correctly.

The Fn+Arrow remapping and SecondaryFn flag logic are thoroughly tested and hardware-validated. The only gap is that direct Home/End key code shortcuts do not get SecondaryFn added automatically unlike Page Up/Down, but this affects only a manually-authored edge case not covered by the docs and does not regress any existing functionality.

The SecondaryFn condition in crates/openlogi-inject/src/inject/macos.rs is worth a second look to decide whether Home/End should be treated consistently with Page Up/Down.

Important Files Changed

Filename	Overview
crates/openlogi-core/src/binding.rs	Adds MOD_FN constant (0x10), prepends fn first in rendered_label, and extends the key_code match table with navigation keys. Tests cover isolated Fn, combined-modifier ordering, and TOML round-trip.
crates/openlogi-inject/src/inject/macos.rs	Extracts custom_shortcut_event helper that translates MOD_FN+Arrow to Home/End/Page Up/Page Down virtual keys with CGEventFlagSecondaryFn. Direct Page Up/Down key codes also get SecondaryFn; Home/End are omitted from that same auto-flag condition.
crates/openlogi-inject/examples/inject_action.rs	Usage string updated to document 0x10=Fn (macOS) modifier bit — one-line docs change, no logic touched.
docs/CONFIGURATION.md	Documents the Fn modifier mask (16) with TOML examples for Fn+Up/Down, and notes Page Up/Down auto-SecondaryFn behavior — accurate and consistent with the implementation.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[CustomShortcut combo] --> B{MOD_FN set?}
    B -->|Yes| C{Is key an arrow?}
    C -->|Up 0x7E| D[Remap to PAGE_UP 0x74]
    C -->|Down 0x7D| E[Remap to PAGE_DOWN 0x79]
    C -->|Left 0x7B| F[Remap to HOME 0x73]
    C -->|Right 0x7C| G[Remap to END 0x77]
    C -->|other| H[Keep key_code as-is]
    D --> I[Add SecondaryFn flag]
    E --> I
    F --> I
    G --> I
    H --> I
    B -->|No| J{key_code is Page Up or Page Down?}
    J -->|Yes| K[Add SecondaryFn flag]
    J -->|No| L[No SecondaryFn flag]
    I --> M[post_key with final key and flags]
    K --> M
    L --> M

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flowchart TD
    A[CustomShortcut combo] --> B{MOD_FN set?}
    B -->|Yes| C{Is key an arrow?}
    C -->|Up 0x7E| D[Remap to PAGE_UP 0x74]
    C -->|Down 0x7D| E[Remap to PAGE_DOWN 0x79]
    C -->|Left 0x7B| F[Remap to HOME 0x73]
    C -->|Right 0x7C| G[Remap to END 0x77]
    C -->|other| H[Keep key_code as-is]
    D --> I[Add SecondaryFn flag]
    E --> I
    F --> I
    G --> I
    H --> I
    B -->|No| J{key_code is Page Up or Page Down?}
    J -->|Yes| K[Add SecondaryFn flag]
    J -->|No| L[No SecondaryFn flag]
    I --> M[post_key with final key and flags]
    K --> M
    L --> M

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