fix: PIN code handling improvements

[clintongormley]

Summary

Follow-up fixes to #326 (AndroidAuto / PIN code feature):

• PIN can now be cleared: Use suggested_value instead of default for the PIN field in the options flow, so clearing the field actually removes the PIN instead of silently restoring it
• Defense-in-depth for arm without PIN: _check_code_for_arm_if_required now skips the PIN check when no PIN is configured, even if code_arm_required is stale True in the config
• Default changed: code_arm_required defaults to False (don't require PIN to arm)
• Clearer label: "Also require PIN code (if any) to arm alarm" makes the dependency on having a PIN explicit
• Missing translation: Added exceptions.invalid_pin_code to strings.json, en.json, and es.json so ServiceValidationError renders properly
• Docstring fix: Grammar correction in _check_code_for_arm_if_required

Test plan

• Set a PIN, verify it's required to disarm
• With PIN set and "require PIN to arm" unchecked, verify arming works without PIN
• With PIN set and "require PIN to arm" checked, verify arming requires PIN
• Clear the PIN in options, verify no PIN is required for any action
• With no PIN and "require PIN to arm" checked, verify arming still works without PIN prompt

🤖 Generated with Claude Code

Relates to #326

[Copilot]

Pull request overview

Follow-up fixes to the Securitas Direct integration’s PIN code feature (introduced/modified in #326), focusing on making PIN clearing work correctly in the options flow and hardening arm/disarm PIN enforcement behavior.

Changes:

• Update options flow PIN field to use suggested_value (so clearing the field can persist) and ensure a missing submission clears the stored PIN.
• Adjust arm-time PIN checking to skip validation when no PIN is configured.
• Update UI labels and add/ensure exception translation strings for invalid PIN errors.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
custom_components/securitas/config_flow.py	Options flow: make PIN value “suggested” (not forced) and normalize missing PIN input to an explicit empty value.
custom_components/securitas/alarm_control_panel.py	Arm-time PIN check now bypasses when no PIN is configured; uses translated ServiceValidationError for invalid PIN.
custom_components/securitas/strings.json	Update label text for code_arm_required and include exception translation for invalid PIN.
custom_components/securitas/translations/en.json	English translation updates for the code_arm_required label and invalid PIN exception message.
custom_components/securitas/translations/es.json	Spanish translation updates for the code_arm_required label and invalid PIN exception message.

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