Ports the subtle text-shadow glow @hive/agent's and the dashboard's own
headline rule already use (both independently converged on
`text-shadow: 0 0 Npx color-mix(color, transparent)`), not their whole
uppercase+letter-spacing headline typography -- that's those UIs' own
look, swarm-ui never adopted it and this issue only asked for the glow.
- Panel titles: `currentColor`-based, since a panel title has no one
fixed accent (some are dynamic, e.g. an agent's own name) -- a fixed
--purple glow on plain --fg text would read as a mismatched halo.
- Active nav tab: each item's own `accent` (NAV_ITEMS), the same value
its underline already uses, so the glow and the underline read as
one accent rather than two that happen to agree.
fefeaecbbf