Copy PDF URL now checks window.isSecureContext before using
navigator.clipboard, falls back to textarea+execCommand on HTTP,
and shows a success notification.
Invoice dropdown: Mark as Sent uses its own condition instead of
reusing Send, Resend hidden in detail view.
Estimate dropdown: Mark as Accepted/Rejected hidden when already in
the other terminal state, Convert to Invoice hidden on rejected
estimates. Added Convert to Estimate action for invoices.
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