refactor: extract plist generation into standalone PlistGenerator

[malpern]

Summary

• Extract all plist generation functions from LaunchDaemonInstaller.swift into a new standalone PlistGenerator struct
• Create pure, stateless static methods for generating launchd plist XML content
• Include all service IDs and executable paths as constants in the new file

Changes

New file Sources/KeyPathAppKit/InstallationWizard/Core/PlistGenerator.swift containing:

• generateKanataPlist() - Creates Kanata service launchd plist
• generateVHIDDaemonPlist() - Creates VHID daemon launchd plist
• generateVHIDManagerPlist() - Creates VHID manager launchd plist
• generateLogRotationPlist() - Creates log rotation service plist
• buildKanataPlistArguments() - Builds Kanata command-line arguments

Test plan

• swift build succeeds with no errors
• swift test passes (all 60 Swift Testing tests pass)
• New file compiles independently
• No changes to existing files (extraction-only)

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Note

Adds a new PlistGenerator with pure static methods to generate launchd plists for Kanata, VHID daemon/manager, and log rotation, plus a Kanata args builder.

• Core (Installation Wizard):
  • New Sources/KeyPathAppKit/InstallationWizard/Core/PlistGenerator.swift:
    • Defines constants for service IDs and executable paths (kanata, vhiddaemon, vhidmanager, logrotate).
    • Adds static generators: generateKanataPlist, generateVHIDDaemonPlist, generateVHIDManagerPlist, generateLogRotationPlist.
    • Adds helper buildKanataPlistArguments for Kanata program args.
    • Produces complete launchd plist XML strings with logging, run behavior, and user/group settings.

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