[CHORE]: Standardize ui-rewrite table column headers on TableHead token defaults

[a-effort]

Summary

Standardize all React (ui-rewrite) data-table column headers on the semantic Tailwind tokens already defined in the base TableHead component (text-xs font-medium text-muted-foreground). Several tables currently override this with arbitrary sizes (text-[13px]) or hardcoded neutrals (text-neutral-600 dark:text-neutral-400), so headers don't read consistently across tabs.

Split out of the #6137 review, which touched Users/Teams headers and surfaced the drift. Kept out of that PR to avoid scope creep.

Parent: #5369

Context / Rationale

The base TableHead (client/src/components/ui/table.tsx:63) already sets the intended default: h-12 px-4 font-medium text-muted-foreground. Most tables conform; two diverge on color, one on size/weight:

Table	Size	Weight	Color
ToolsTable	text-xs	font-medium	inherits text-muted-foreground ✅
ResourcesTable	text-xs	font-medium	inherits text-muted-foreground ✅
PromptDefinitionTable	text-xs	font-medium	inherits text-muted-foreground ✅
ServersTable	text-xs	font-medium	text-neutral-600 dark:text-neutral-400 ❌
TeamsTable	text-xs	font-medium	text-neutral-600 dark:text-neutral-400 ❌
UsersTable	text-[13px]	font-normal	text-muted-foreground (size/weight ❌)

Impact: the text-neutral-600 override makes Servers/Teams headers darker than other tables in light mode (#525252 vs the muted-foreground token; dark mode matches). UsersTable's text-[13px] font-normal renders its headers at a different size/weight from all the others.

This standardizes on the token/codebase conventiontext-xs (12px medium). Figma mockups use slightly different styles, but proposing we get consistency first then make any tweaks in one pass later on, if desired.

Scope / Changes

• ServersTable.tsx, TeamsTable.tsx: remove text-neutral-600 dark:text-neutral-400 so headers inherit text-muted-foreground.
• UsersTable.tsx: replace text-[13px] font-normal leading-4 with text-xs font-medium; reconcile h-[52px] toward the base h-12 (confirm against row rhythm first).
• Delete overrides that restate the base default rather than re-adding them.
• Visual-consistency only; no behavioral change.

Acceptance Criteria

• All six ui-rewrite tables render headers at text-xs, font-medium, text-muted-foreground in light and dark mode.
• No table re-declares the base default via arbitrary values or hardcoded neutrals for header type/color.
• cd client && npm run lint && npx tsc --noEmit clean.
• Affected header-class assertions updated (e.g. Users.test.tsx).