style(visual-fidelity): components — batches B,E,G,H

- B: token-equivalent rgba → color-mix in SignupFlowOverlay, OnboardingWidget
- E: drop text-white Tailwind utility from ImageUpload remove-button (now color: var(--parch-text) inline)
- G: typography off-scale snaps (9→10, 14→13, 15→16, 19→18 px)
- H: padding off-scale snaps in BoardPostCard/Form, CirclePicker, FilterBar, LoginModal

app/components/CirclePicker.vue

@@ -48,7 +48,7 @@ defineEmits(['update:modelValue'])
 
 .circle-option {
   border: 1px dashed var(--border);
-  padding: 14px 12px;
+  padding: 12px 12px;
   background: var(--bg);
   cursor: pointer;
   transition: all 0.15s;
@@ -83,7 +83,7 @@ defineEmits(['update:modelValue'])
 }
 
 .circle-tag {
-  font-size: 9px;
+  font-size: 10px;
   letter-spacing: 0.06em;
   text-transform: uppercase;
   margin-top: 6px;