WIP - style: flatten light-theme surfaces and unify elevation

[a-effort]

Follow-up to #34. Light theme is flat by design: surfaces get no elevation, controls carry none in either theme, and floating layers keep theirs.

Why a token

Tailwind inlines shadow values at build time — only the color is a variable, and --tw-shadow-color is registered inherits: false — so there is no single place to switch shadows off per theme. src/index.css gains four utilities that read a variable instead:

token	light	dark
elevation-xs	flat	Tailwind's shadow-xs
elevation-sm	flat	Tailwind's shadow-sm
elevation-panel	flat	the form-panel shadow
elevation-control	raised	raised

Dark mode keeps the exact values the raw utilities used, so nothing shifts there.

They compose through --tw-shadow rather than setting box-shadow directly. This matters: ring-* builds its outline from the same box-shadow list, and .elevation-* is emitted after .ring-1, so setting the property outright erased the ring on every card in light mode.

Three rules

• controls — no shadow in either theme: buttons, inputs, switches, select triggers.
• surfaces — elevation-*: cards, form panels, toolbars, icon chips.
• floating — untouched: popovers, dropdowns, dialogs, sheets, the five slide-over detail panels.

elevation-control is the deliberate exception. Flattening the selected chip of a segmented control loses what makes it read as selected, so it stays raised in both themes. All 13 segmented controls in the app now share it — previously they split across two shadow levels and a dark-fill variant.

Also here

• Two forms aligned. The create-server form adopted the connect-MCP-server form's chrome: card border/padding/elevation, icon chip, heading and intro type, inputs, disclosure toggle, and footer buttons. That fixed a pre-existing bg-white text-black submit button that was invisible against the light card, and dropped five one-off hex literals (#141414, #2b2b2f, #55555c, #252529, #343438).
• Placeholders on the token. 17 fields across the MCP server form and its auth panels moved from hardcoded neutral-400/neutral-500 to text-muted-foreground — more legible in both themes. ~12 overrides remain in the tools/resources/prompts forms; see the note below.
• Disclosure toggles no longer fill. variant="ghost" carries aria-expanded:bg-muted, so Optional configuration and Advanced settings filled whenever expanded.
• Add resources chip now uses the tool-add-icon tokens like its siblings, instead of a hardcoded gray.
• CA certificate Upload button is ghost, dropping six hardcoded neutrals.
• Two dead sidebar shadows. shadow-[0_0_0_1px_hsl(var(--sidebar-border))] resolves to hsl(oklch(...)) after the token migration, which is invalid — that outline has not been rendering. Replaced with ring-*.

Testing

2841 unit tests pass; tsc --noEmit, eslint, and prettier --check clean. One test needed updating: input.test.tsx asserted the input carries shadow-xs.

The utilities were verified against the emitted CSS — light resolves to 0 0 #0000, dark to the original Tailwind values byte-for-byte, and all four variant forms (aria-pressed:, peer-checked:, data-[state=active]:, data-[state=checked]:) compile.

This is a visual change and the tests do not cover it. Both regressions caught during development — the ring clobbering above, and a card that went white in dark mode — were found by eye, not by CI. Worth a pass through both themes before merge.

Not included

• Form-card fills. Giving the eleven form panels their own surface colour, and retargeting --card (which currently equals --main exactly, so bg-card gives no separation from the page). Parked on form-card-fill; needs rework.
• ui/input and ui/textarea disagree on placeholder colour — the token vs. hardcoded neutrals, running opposite to each other. ~12 per-form overrides work around it. Fixing it in textarea.tsx is one line but touches every textarea.
• 47 now-dead shadow-none overrides, left over from cancelling shadows the primitives no longer have.