The previous `<img src="/icons/config/security.svg">` icon hardcoded
`stroke="#1e90ff"` (dodger blue) rather than `currentColor`, so on
themes where it should pick up the sidebar foreground colour it just
disappeared or visually clashed. The other Tools / admin sidebar items
(Overview, System, Peers) all use inline SVGs with `stroke=currentColor`
and follow the theme correctly.
Switched SSH Access to an inline key icon in the same style — circle
shackle bottom-left, shaft going up-right to a notched bit. Matches the
'what is this thing' framing: an SSH access page is fundamentally about
managing keys.
security.svg itself is left untouched (might be used elsewhere).
Signed-off-by: librelad <librelad@digitalangels.vip>