Fix webhook delivery and callback crash on HA 2026.5

[sevorl]

What this fixes

Webhook automations not triggering reliably on HA Core 2026.5+ (notably with local_only true).
Runtime crash on incoming/registration callbacks:
AttributeError: Account object has no attribute onRegState
Changes

Added dedicated webhook base URL support (HA_WEBHOOK_BASE_URL) and wired it through config/runtime.
In add-on mode, default webhook endpoint now targets Core directly via homeassistant hostname.
Implemented webhook delivery fallback chain with better logging and exception handling.
Fixed pjsua2 callback dispatch compatibility by explicitly binding callback handlers on Account instances.
Enforced LF line endings for shell scripts via .gitattributes to prevent bash carriage-return startup failures.
Added/updated tests for webhook URL selection and send behavior.
Updated README with webhook base URL behavior.
Validation

Reproduced and fixed startup failure caused by CRLF shell scripts.
Verified webhook-triggered automations fire again in HA OS test deployment.
Verified focused webhook unit tests pass.
Issue
Closes #197

[arnonym]

Hi,

this PR mixes fixes for several issues into one.

1. Attribute errors.
2. Web-hook problem
3. CRLF shell script.

For 1. and 2. I never saw a bug report and I also did not experience that error. Where does this come from?

For 2: the fix will trigger the web-hook multiple times for different URLs. That does not make any sense to me.

And also this PR looks very much AI generated. Was any of this tested locally?

Regards,
Arne

[sevorl]

Hi @arnonym,
thanks for reviewing this pr.
While testing the webhook fix, I noticed that the app crashed and therefore added these additional fixes.

Yes, I did this with AI assistance.
I tested this locally and use this version for two days now on my system. I did not notice any issues and just double checked the logs.