Delete cloudhook on config entry removal

[jbergler]

Summary

• async_remove_entry now calls cloud.async_delete_cloudhook when a TTLock config entry is removed, closing a permanent leak in Nabu Casa cloud prefs for cloud users
• Checks that no sibling config entry still shares the removed entry's webhook_id (entries can share one webhook per developer application, see docs/adr/0002-shared-webhook-per-developer-application.md) before deleting
• Suppresses ValueError alongside cloud.CloudNotAvailable, since hass_nabucasa raises a bare ValueError when the webhook_id was never actually converted to a cloudhook — same gap HA core's mobile_app integration already works around

Fixes #316

Test plan

• script/check passes (lint, type-check, 251 tests)
• New tests cover all three acceptance criteria: last-entry-sharing removal deletes the cloudhook, removal of one of several sharing entries does not, and removal is a no-op (not an error) both for non-cloud users and for cloud users whose webhook was never converted to a cloudhook

🤖 Generated with Claude Code

https://claude.ai/code/session_01PvyPWXq9s7xw1L3fkphDGc

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.00%. Comparing base (aee79af) to head (f037b3f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
custom_components/ttlock/__init__.py	92.85%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #317      +/-   ##
===========================================
+ Coverage    95.97%   96.00%   +0.03%     
===========================================
  Files           17       17              
  Lines         1589     1602      +13     
===========================================
+ Hits          1525     1538      +13     
  Misses          64       64              

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