fix(#94): replace text-white with text-primary-fg on all primary buttons

In dark mode --c-primary switches from navy (#012851) to mint (#a1dcd8).
Buttons using bg-primary+text-white showed white text on mint at 1.4:1
contrast — invisible. bg-brand-navy buttons were also invisible (navy on
near-black canvas, 1.3:1).

Replaced in 28 components app-wide:
- bg-primary ... text-white → text-primary-fg
- hover:bg-primary hover:text-white → hover:text-primary-fg
- bg-brand-navy ... text-white + hover:bg-brand-navy/90 →
  bg-primary ... text-primary-fg + hover:bg-primary/90

Light mode is unchanged: primary-fg = white in light mode.
Dark mode: primary-fg = navy (#012851) on mint bg = readable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/admin/+page.svelte

@@ -20,28 +20,28 @@ let activeTab = $state('users');
 			<button
 				class="rounded-md px-2 py-2 text-sm font-bold tracking-wide uppercase transition sm:px-4 {activeTab ===
 				'users'
-					? 'bg-primary text-white'
+					? 'bg-primary text-primary-fg'
 					: 'text-ink-2 hover:text-ink'}"
 				onclick={() => (activeTab = 'users')}>{m.admin_tab_users()}</button
 			>
 			<button
 				class="rounded-md px-2 py-2 text-sm font-bold tracking-wide uppercase transition sm:px-4 {activeTab ===
 				'groups'
-					? 'bg-primary text-white'
+					? 'bg-primary text-primary-fg'
 					: 'text-ink-2 hover:text-ink'}"
 				onclick={() => (activeTab = 'groups')}>{m.admin_tab_groups()}</button
 			>
 			<button
 				class="rounded-md px-2 py-2 text-sm font-bold tracking-wide uppercase transition sm:px-4 {activeTab ===
 				'tags'
-					? 'bg-primary text-white'
+					? 'bg-primary text-primary-fg'
 					: 'text-ink-2 hover:text-ink'}"
 				onclick={() => (activeTab = 'tags')}>{m.admin_tab_tags()}</button
 			>
 			<button
 				class="rounded-md px-2 py-2 text-sm font-bold tracking-wide uppercase transition sm:px-4 {activeTab ===
 				'system'
-					? 'bg-primary text-white'
+					? 'bg-primary text-primary-fg'
 					: 'text-ink-2 hover:text-ink'}"
 				onclick={() => (activeTab = 'system')}>{m.admin_tab_system()}</button
 			>

frontend/src/routes/admin/GroupsTab.svelte

@@ -212,7 +212,7 @@ function cancelEditGroup() {
 
 			<button
 				type="submit"
-				class="w-full rounded bg-primary px-6 py-2 text-sm font-bold text-white uppercase hover:bg-accent hover:text-ink md:w-auto"
+				class="w-full rounded bg-primary px-6 py-2 text-sm font-bold text-primary-fg uppercase hover:bg-accent hover:text-ink md:w-auto"
 			>
 				{m.btn_create()}
 			</button>

frontend/src/routes/admin/SystemTab.svelte

@@ -41,7 +41,7 @@ async function backfillFileHashes() {
 	<button
 		onclick={backfillVersions}
 		disabled={backfillLoading}
-		class="rounded bg-primary px-6 py-2 text-sm font-bold text-white uppercase transition hover:bg-accent hover:text-ink disabled:cursor-not-allowed disabled:opacity-50"
+		class="rounded bg-primary px-6 py-2 text-sm font-bold text-primary-fg uppercase transition hover:bg-accent hover:text-ink disabled:cursor-not-allowed disabled:opacity-50"
 	>
 		{backfillLoading ? '…' : m.admin_system_backfill_btn()}
 	</button>
@@ -60,7 +60,7 @@ async function backfillFileHashes() {
 	<button
 		onclick={backfillFileHashes}
 		disabled={backfillHashesLoading}
-		class="rounded bg-primary px-6 py-2 text-sm font-bold text-white uppercase transition hover:bg-accent hover:text-ink disabled:cursor-not-allowed disabled:opacity-50"
+		class="rounded bg-primary px-6 py-2 text-sm font-bold text-primary-fg uppercase transition hover:bg-accent hover:text-ink disabled:cursor-not-allowed disabled:opacity-50"
 	>
 		{backfillHashesLoading ? '…' : m.admin_system_backfill_hashes_btn()}
 	</button>

frontend/src/routes/admin/UsersTab.svelte

@@ -20,7 +20,7 @@ let {
 		<h2 class="text-lg font-bold text-ink-2">{m.admin_section_users()}</h2>
 		<a
 			href="/admin/users/new"
-			class="inline-flex items-center gap-1 rounded-sm bg-primary px-4 py-2 font-sans text-xs font-bold tracking-widest text-white uppercase transition-opacity hover:opacity-80"
+			class="inline-flex items-center gap-1 rounded-sm bg-primary px-4 py-2 font-sans text-xs font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-80"
 		>
 			<svg class="h-4 w-4" fill="none" stroke="currentColor" viewBox="0 0 24 24">
 				<path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 4v16m8-8H4" />

frontend/src/routes/admin/users/[id]/+page.svelte

@@ -85,7 +85,7 @@ const selectedGroupIds = $derived(data.editUser.groups?.map((g: { id: string })
 			</a>
 			<button
 				type="submit"
-				class="rounded-sm bg-primary px-5 py-2 font-sans text-xs font-bold tracking-widest text-white uppercase transition-opacity hover:opacity-80"
+				class="rounded-sm bg-primary px-5 py-2 font-sans text-xs font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-80"
 			>
 				{m.btn_save()}
 			</button>

frontend/src/routes/admin/users/new/+page.svelte

@@ -61,7 +61,7 @@ let { data, form } = $props();
 				</a>
 				<button
 					type="submit"
-					class="rounded-sm bg-primary px-5 py-2 font-sans text-xs font-bold tracking-widest text-white uppercase transition-opacity hover:opacity-80"
+					class="rounded-sm bg-primary px-5 py-2 font-sans text-xs font-bold tracking-widest text-primary-fg uppercase transition-opacity hover:opacity-80"
 				>
 					{m.btn_create()}
 				</button>