fix: use --color-text-on-primary for all primary button text

Replace hardcoded white/#fff text on --color-primary buttons with
var(--color-text-on-primary) for proper theme contrast across:
- nutrition meals page (create btn + modal buttons)
- history detail page (save btn + start workout btn)
- recipe page (active filter chips)
- nutrition quick-log confirm button

src/routes/[recipeLang=recipeLang]/+page.svelte

@@ -273,7 +273,7 @@
 }
 .chip.active {
 	background: var(--color-primary);
-	color: white;
+	color: var(--color-text-on-primary);
 }
 .chip.season {
 	background: var(--color-accent);

src/routes/fitness/[history=fitnessHistory]/[id]/+page.svelte

@@ -843,7 +843,7 @@
 	}
 	.save-btn {
 		background: var(--color-primary);
-		color: white;
+		color: var(--color-text-on-primary);
 		border: none;
 		border-radius: 8px;
 		padding: 0.4rem 1rem;
@@ -1057,7 +1057,7 @@
 		width: 100%;
 		padding: 0.75rem;
 		background: var(--color-primary);
-		color: white;
+		color: var(--color-text-on-primary);
 		border: none;
 		border-radius: 10px;
 		font-weight: 700;

src/routes/fitness/[nutrition=fitnessNutrition]/+page.svelte

@@ -3725,7 +3725,7 @@
 		border: none;
 		border-radius: 6px;
 		background: var(--color-primary);
-		color: white;
+		color: var(--color-text-on-primary);
 		cursor: pointer;
 		transition: filter 0.12s;
 	}

src/routes/fitness/[nutrition=fitnessNutrition]/meals/+page.svelte

@@ -358,8 +358,8 @@
 		display: flex;
 		align-items: center;
 		gap: 0.35rem;
-		background: var(--nord8);
-		color: #fff;
+		background: var(--color-primary);
+		color: var(--color-text-on-primary);
 		border: none;
 		border-radius: 8px;
 		padding: 0.5rem 0.85rem;
@@ -369,7 +369,7 @@
 		transition: background 0.15s;
 	}
 	.create-btn:hover {
-		background: var(--nord10);
+		background: var(--color-primary-hover);
 	}
 
 	/* ── Loading ── */
@@ -700,11 +700,11 @@
 		cursor: default;
 	}
 	.btn.primary {
-		background: var(--nord8);
-		color: #fff;
+		background: var(--color-primary);
+		color: var(--color-text-on-primary);
 	}
 	.btn.primary:hover:not(:disabled) {
-		background: var(--nord10);
+		background: var(--color-primary-hover);
 	}
 	.btn.secondary {
 		background: var(--color-bg-tertiary);