feat: add configurable target-agent profiles

[sparkg]

What changed

• replace the hard-coded macro with one AgentProfile -> resolveSteps(platform) -> InputDriver.execute path
• keep Claude Code as the default profile and add a Codex profile that sends message -> Enter for both CLI and Desktop workflows
• add an explicit Target Agent tray selector, persisted selection, configurable custom profiles, serialized state mutations, and atomic profile reloads
• translate the allowlisted keystroke, message, and delay actions for Windows, macOS, and Linux without adding dependencies
• use Unicode SendInput for Windows messages while retaining portable keystrokes, and normalize custom letter keys at the schema boundary
• add a Windows/macOS/Ubuntu GitHub Actions matrix for installation, tests, syntax checks, and package inspection
• document the versioned JSON format, limits, ASCII-only messages, and foreground-window scope

OpenWhip still does not detect the active Agent. Users explicitly choose a profile, and custom configuration cannot execute shell commands, JavaScript, or external scripts.

Validation

• npm test — 33 tests passed locally and on all three hosted operating systems
• Cross-platform GitHub Actions run — windows-latest, macos-latest, and ubuntu-latest all passed
• every matrix job completed npm ci, npm test, JavaScript syntax checks, and npm pack --dry-run
• package inspection reports 18 files, includes lib/, and excludes tests and local development context
• automated fake-driver coverage verifies Windows FFI calls, macOS AppleScript, and Linux xdotool arguments
• git diff --check

The hosted matrix verifies Node behavior, platform-action translation, dependency installation, and packaging on all three operating systems. It does not exercise real global keyboard injection, desktop focus, accessibility permissions, or a live Agent application; those remain platform-specific manual checks.

Relationship to existing PRs

• #25 automatically routes by the active macOS application and also changes package/security/dependency scope. This PR uses explicit profile selection, does no process detection, and leaves package identity and dependency versions unchanged.
• #23 adds visual modes and hotkeys. This PR does not modify the overlay or preload bridge; it only generalizes target input behavior, so the designs are independent.