Add ascent-chekhov typed locators for JSEnv and JVM Page

[russwyte]

Closes #64.

Replaces Chekhov's thin chekhov-ascent mount bridge in this repo. Tests talk to nodes as InputHandle / ButtonHandle instead of org.scalajs.dom.Element.

Summary

• New published ascent-chekhov (JVM + JS): shared HtmlTag / TagHandle lattice, JSEnv withMounted + live handles, JVM PageHandles over Chekhov Locator.
• fill is only on input-like handles. Catalog vals stay unparameterized ElementKey; pass HtmlTag.button or root.button("inc").
• Bump Chekhov / sbt-chekhov to 0.0.5. JSEnv suites run on the existing e2e zipx job, not testJS.
• HybridChat e2e uses PageHandles.getByPlaceholder(..., HtmlTag.input).
• Follow-up to delete chekhov-ascent after the next Ascent release: Remove chekhov-ascent; Ascent owns the mount + typed locators chekhov#38.

Test plan

Covered by CI (ascentChekhov on testJVM; ascentChekhovJS/testFull on the e2e job). Locally:

• sbt ascentChekhov/testFull
• sbt "e2e/chekhovInstall; ascentChekhovJS/testFull"
• sbt e2e/testFull