Fix form control consistency; add frontend style guide

- QuantityInput unit select: add bg-white (browser defaults to gray
  without it) and capitalize default option to "Unit"
- Shopping list section dropdowns: rename "Uncategorized" → "No section"
  for consistent title-case phrasing across all default options
- src/frontend/STYLE_GUIDE.md: documents form control classes, button
  variants, text casing rules, icon usage, color tokens, and spacing
  rhythm so all future UI work stays consistent
- CLAUDE.md: link to the style guide so it is always consulted

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -88,6 +88,8 @@ When adding a feature: create `Features/<Name>/<Name>Endpoints.cs` with a `Map<N
 
 ### Frontend — SvelteKit with runes
 
+**UI consistency:** all form controls, buttons, colors, icons, spacing, and text casing are governed by `src/frontend/STYLE_GUIDE.md`. Read it before adding or modifying any UI component — deviating without a documented reason is a bug.
+
 - `svelte.config.js` forces `runes: true` for all non-`node_modules` files. Use Svelte 5 runes (`$state`, `$derived`, `$effect`); do not use legacy reactive `$:` syntax.
 - `src/lib/api.ts` — `api<T>(path, opts)` helper. Stores the JWT in `localStorage` under `token`, attaches `Authorization: Bearer …`, and on 401 it clears the token and `goto('/login')`.
 - `src/lib/auth.svelte.ts` — runes-based auth state.

src/frontend/STYLE_GUIDE.md

@@ -0,0 +1,71 @@
+# Frontend Style Guide
+
+Rules that apply to every component. Deviating from these requires an explicit reason.
+
+## Form controls
+
+All interactive inputs, selects, and textareas share one baseline class set so they look identical regardless of type:
+
+```
+rounded-lg border border-gray-300 bg-white px-3 py-2 text-sm
+focus:border-primary focus:outline-none
+```
+
+| Variant | When to use | Size note |
+|---|---|---|
+| **Standard** (`px-3 py-2`) | Inline rows (qty, unit, section dropdowns, filters) | `text-sm` |
+| **Large** (`px-3 py-2.5 text-base`) | Full-width, standalone inputs (item name, recipe title) | `text-base` |
+
+**Rules:**
+- `bg-white` is **always explicit** on `<select>` — browsers default to gray without it.
+- Never mix `py-2` and `py-2.5` controls in the same flex row; they will be different heights.
+- Fixed-width selects (unit dropdown: `w-24`, qty: `w-20`). Unconstrained selects get `max-w-36` so long option text doesn't push other controls off screen.
+
+## Buttons
+
+| Style | Class | Use |
+|---|---|---|
+| Primary | `rounded-lg bg-primary px-4 py-2 font-semibold text-white` | Main action (Add, Save Changes) |
+| Secondary | `rounded-lg border border-gray-300 px-4 py-2 text-sm text-gray-700` | Peer to primary (Cancel, Edit) |
+| Danger (inline) | `rounded-lg border border-danger px-4 py-2 text-sm text-danger` | Destructive, same visual weight as secondary |
+| Danger (footer) | `text-sm text-danger hover:underline` | Low-prominence delete at the bottom of a detail page |
+| Ghost | `text-sm text-gray-500` | Back links, minor navigation |
+
+Primary and secondary buttons that appear in the same row must use the same `py-*` value.
+
+## Text casing
+
+| Context | Rule | Example |
+|---|---|---|
+| Button labels | Title Case | `Save Changes`, `Add`, `Cancel` |
+| Placeholder text | Sentence case | `Add an item...`, `Recipe title` |
+| Select default option | Title Case | `Unit`, `No section` |
+| Section/group headings | UPPERCASE via `uppercase` CSS class | `UNCATEGORIZED` |
+| Navigation labels | Title Case | `Lists`, `Recipes` |
+| Error / hint text | Sentence case | `~ approximate (e.g. to taste)` |
+
+Never use ALL CAPS in raw text — apply the `uppercase` Tailwind class to let CSS handle it.
+
+## Icons
+
+- Use Heroicons outline style, 16×16 (`h-4 w-4`), `stroke-width="1.75"`.
+- Always include `aria-hidden="true"` on decorative SVGs; the wrapping button carries the `aria-label`.
+- Trash icon for destructive remove actions. No other icon for that purpose.
+
+## Colors
+
+Defined as CSS custom properties in `app.css`. Never hard-code hex values in component classes.
+
+| Token | Use |
+|---|---|
+| `primary` | Brand green — CTAs, active states, quantity highlights |
+| `danger` | Destructive actions, error text |
+| `gray-300` | Default border on all form controls |
+| `gray-400` | Secondary / hint text |
+| `gray-500` | Ghost button text, tertiary labels |
+
+## Spacing rhythm
+
+- Gap between inline form controls in a row: `gap-2`.
+- Gap between stacked form sections: `space-y-2` or `space-y-4`.
+- Card / list item padding: `px-3 py-3` (shopping list) or `px-3 py-2` (compact).

src/frontend/src/lib/QuantityInput.svelte

@@ -92,9 +92,9 @@
 			value={composite}
 			onchange={onUnitChange}
 			aria-label="Unit"
-			class="w-24 rounded-lg border border-gray-300 px-1 py-2 text-sm focus:border-primary focus:outline-none"
+			class="w-24 rounded-lg border border-gray-300 bg-white px-1 py-2 text-sm focus:border-primary focus:outline-none"
 		>
-			<option value="">unit</option>
+			<option value="">Unit</option>
 			{#each visible as unit}
 				<option value="{unit.kind}:{unit.id}">{unit.abbreviation}</option>
 			{/each}

src/frontend/src/routes/lists/[id]/+page.svelte

@@ -302,7 +302,7 @@
 						class="max-w-36 rounded-lg border border-gray-300 bg-white px-2 py-2 text-sm focus:border-primary focus:outline-none"
 						aria-label="Section"
 					>
-						<option value={null}>Uncategorized</option>
+						<option value={null}>No section</option>
 						{#each sections as section (section.id)}
 							<option value={section.id}>{section.name}</option>
 						{/each}
@@ -356,7 +356,7 @@
 											class="shrink-0 rounded border border-gray-200 bg-white px-1 py-0.5 text-xs text-gray-500 focus:border-primary focus:outline-none"
 											aria-label="Section for {item.name}"
 										>
-											<option value="">Uncategorized</option>
+											<option value="">No section</option>
 											{#each sections as section (section.id)}
 												<option value={section.id}>{section.name}</option>
 											{/each}