Fix colon-free hx-on handlers for compound htmx events

[sergioperezcheco]

Description

Fixes #2614. Colon-free handlers such as hx-on--validation-validate currently miss htmx:validation:validate, so custom validity checks never run and invalid values can be submitted. Dispatch a distinct dash-separated alias for compound htmx event names, preserving canonical/camel-case aliases, shared detail, and cancellation ordering. Non-htmx custom event names are unchanged. This also covers hx-on--xhr-progress and documents both spellings.

Testing

The new regression file fails against unchanged production: 20 passing, 6 failing. With the fix, the complete upstream browser harness passes in headless Chromium: 877 passing, 3 skipped across 50 files. Lint, format, type checking, and the official distribution build pass. An independent DOM probe checks alias order, shared detail, cancellation, and custom-event compatibility; a real local HTTP form probe fails on the baseline and passes with both ordinary and minified official builds, blocking invalid submissions while allowing valid submissions.

The browser harness uses the existing Chromium executable through a launcher override. Literal npm run test, Firefox/WebKit, and other OS/Node matrices were not run; remote CI is pending. Prepared and tested autonomously with AI assistance; no human review has occurred.

Checklist

• I have read the contribution guidelines
• I have targeted dev for source changes
• This is a bugfix for documented behavior
• I ran the test suite locally using the literal npm run test command