Copilot review round 1. With an ID Token row alongside the Access Token
row, both can render a "Decode JWT" toggle and a "Copy" control, and the
four buttons shared two accessible names — button-by-button screen-reader
navigation could not tell which token a control acted on. That collision
is introduced by this PR: before it there was only ever one token row.
- `CopyButton` takes an optional `label` naming what is being copied,
used for the accessible name only ("Copy ID Token"). The visible
tooltip stays "Copy", and the name keeps "Copy"/"Copied" as its first
word so it still contains the visible text (WCAG 2.5.3 Label in Name).
- `OAuthTokenField` qualifies its decode toggle the same way ("Decode JWT
for Access Token") and passes its row label down to `CopyButton`.
The visible UI is unchanged — this is accessible-name only.
Signed-off-by: cliffhall <cliff@futurescale.com>