[CL-1129] Enable @angular-eslint/template/elements-content lint rule (#19505)

* Enable @angular-eslint/template/elements-content lint rule

Enables the elements-content rule with bitIconButton exempted via allowList,
since icon buttons use that directive in place of text content. Suppresses
false positives in WebAuthn connector pages where content is injected at
runtime, and flags a genuine empty <a> in change-plan-dialog for follow-up.

* Add FIXME lint suppressions for elements-content in copy-click spec

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Co-authored-by: claude[bot] <41898282+claude[bot]@users.noreply.github.com>