docs: link Help view to central documentation

[yellowcooln]

Summary

Replace the Repeater Help view's obsolete GitHub Wiki destination with the canonical
openHop Repeater documentation:

https://docs.openhop.dev/projects/openhop-repeater/

This updates the heading, explanatory copy, and button label so the interface no
longer describes the destination as a Wiki. A focused component test locks the URL,
labels, and safe external-link attributes.

Related documentation migration

The destination content was published through
openHop_docs#11.

The corresponding backend documentation-link cleanup is tracked in
openhop_repeater#386.
That backend PR intentionally does not hand-edit generated files under
repeater/web/html; this RepeaterUI repository is the authoritative frontend source.
A future backend UI integration/build can consume this corrected source without the
old Wiki link returning on the next rebuild.

Verification

• Focused HelpView Vitest: passed.
• Vue type-check: passed.
• ESLint for changed files: passed.
• Prettier check for changed files: passed.
• Isolated Vite production build: passed.
• The isolated build did not modify the sibling Repeater backend worktree.
• No obsolete Wiki URL or Wiki label remains in RepeaterUI source.
• git diff --check: passed.

The complete unit suite currently has one unrelated failure in
tests/navItem.test.ts (highlights only the matching leaf — not the parent groups).
The same failure was reproduced from a clean export of upstream dev; this Help-view
change does not modify navigation components or that test.