feat: history tab, configurable hotkey, clipboard control

[nicremo]

Summary

Adds a persistent dictation history, configurable hotkey with Fn key support, optional clipboard copying, and several critical bug fixes. All features are backwards-compatible.

Depends on: #6 (right Option key, handsfree, UI upgrades), #5 (dictionary), #4 (cloud transcription)

History Tab

• New History tab in the sidebar (between Dictionary and Preferences)
• Every dictation is saved automatically with: final text, raw transcription, transcription source, style mode, enhancement level, target app name, timestamp
• Expandable entries: click to reveal raw transcription diff, style/level info, and action buttons
• Copy / Copy raw / Remove buttons per entry, Clear all to wipe history
• Live refresh: History tab updates instantly after each dictation via history:updated IPC broadcast to all windows
• Thread-safe JSON persistence with async file lock, auto-capped at 500 entries
• Stored in history.json in the Electron userData directory

Configurable Dictation Hotkey

• Fn key as default (Preferences toggle: "Use Fn key")
• Custom hotkey recorder: click the button, press any key or combination (e.g. Cmd+Option, Shift+Space, right Option)
• Supports three modes: single modifier key, modifier combo, and regular key with modifiers
• Swift helper dynamically accepts keyCode + modifiers as CLI arguments
• Hotkey listener auto-restarts when the shortcut changes
• src/shared/hotkeys.ts: macOS key code mappings, modifier flags, label builder

Optional Clipboard Copying

• New "Copy to clipboard" toggle in Preferences (default: off)
• When off and auto-paste is on: clipboard is used temporarily for Cmd+V, then cleared after 500ms
• When off and auto-paste is off: clipboard is never touched (text only in history)
• Status messages reference history instead of clipboard

Bug Fixes

• Clipboard race condition: clipboard restore executed before target app processed Cmd+V. Root cause: CGEvent post(tap:) is fire-and-forget, the Swift process exits before the target app reads the clipboard. Fix: clear clipboard after 500ms delay instead of immediate restore.
• Listening stuck active: short key taps (< 300ms) started recording even after key release. Root cause: double-click timer ignored the up event, then fired handleHotkeyDown with no subsequent up to stop it. Fix: track physical key state via keyHeldRef and cancel recording if key was released when timer fires.
• Double-click regression: the listening fix initially broke double-click detection for handsfree mode. Root cause: timer was cancelled on up event, preventing the second down from recognizing a double-click. Fix: only set keyHeldRef = false on up, do not cancel the timer.

What changed

File	Change
src/shared/hotkeys.ts	New: key code mappings, modifier flags, Fn key constants, label builder
src/shared/types.ts	HotkeyConfig, HistoryEntry, copyToClipboard in AppSettings
src/main/history.ts	New: load/add/remove/clear with async lock, 500 entry cap
src/main/dictation.ts	Clipboard logic rewrite (race fix), style/enhancement in result
src/main/ipc.ts	History handlers, broadcast dependency, hotkey restart on settings change
src/main/native-helper.ts	HotkeyConfig passed to Swift listener as CLI args
src/main/index.ts	restartHotkeyListener, broadcast to IPC dependencies
src/main/defaults.ts	Fn key as default hotkey, copyToClipboard: false
src/preload/index.ts	History bridge, onHistoryUpdated listener
src/renderer/env.d.ts	Window types for history and hotkey
src/renderer/App.tsx	HistoryPage, HotkeyRecorder with Fn toggle, live history refresh, keyHeldRef fix
src/renderer/styles.css	History entries, hotkey recorder styles
swift/OpenWhispHelper.swift	Configurable keyCode/modifiers, Fn key (maskSecondaryFn), 3 hotkey modes

Test plan

• History: dictate something, entry appears in History tab immediately (live refresh)
• History: click entry to expand, shows raw transcription and style info
• History: Copy / Copy raw / Remove buttons work
• History: Clear all removes everything, shows empty state
• History: quit and reopen, entries persist
• Hotkey Fn: toggle "Use Fn key" on, hold Fn to dictate
• Hotkey custom: toggle Fn off, click recorder, press right Option, verify it works
• Hotkey combo: record Cmd+Option as hotkey, verify dictation starts with combo
• Hotkey restart: change hotkey in Preferences, verify new key works immediately
• Clipboard off + paste on: dictation pastes correctly, clipboard is empty after 500ms
• Clipboard on + paste on: dictation pastes correctly, text stays in clipboard
• Clipboard off + paste off: clipboard untouched, text only in history
• Listening bug: short tap (< 300ms) must NOT start recording
• Double-click: double-tap hotkey enters handsfree mode, single tap to exit
• Hold: hold hotkey > 300ms, speak, release to process