Enhance E2E tests to verify bin file executability

[groupsky]

Problem

E2E tests currently check that bin files exist but not that they are executable:

@test "emulator CLI binary exists" {
  [ -f "../../packages/emulator/dist/esm/bin/ya-modbus-emulator.js" ]
}

This test would pass even if the file has no executable permissions.

Context

• E2E tests invoke bins with node <path>, bypassing executable permissions
• This means bins could ship without executable permissions and tests would still pass
• Real users expect to run ya-modbus-emulator directly, not node ya-modbus-emulator.js

Proposed Solution

Update E2E tests to check executability instead of just existence:

tests/e2e/tests/02-emulator.bats:

@test "emulator CLI binary is executable" {
  [ -x "../../packages/emulator/dist/esm/bin/ya-modbus-emulator.js" ]
}

@test "emulator CLI binary can be invoked directly" {
  run ../../packages/emulator/dist/esm/bin/ya-modbus-emulator.js --version
  assert_success
}

Apply similar changes to:

• tests/e2e/tests/03-mqtt-bridge.bats
• tests/e2e/tests/04-cli.bats
• tests/e2e/tests/05-device-profiler.bats (if exists)

Benefits

• Tests match real-world usage (direct invocation, not via node)
• Catches permission issues before they reach production
• More accurate validation of CLI behavior

Effort

~1 hour (update 3-4 test files)

Related

• Convert @ya-modbus/emulator to TypeScript-built bin for consistency #361 (standardized build process)
• fix(build): set executable permissions on CLI bin files #359 (added chmod to build scripts)