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/BoardPostForm.vue

@@ -138,7 +138,7 @@ function handleSubmit() {
 <style scoped>
 .post-form {
   border: 1px dashed var(--border);
-  padding: 14px 16px;
+  padding: 16px 16px;
   background: transparent;
 }
 
@@ -147,7 +147,7 @@ function handleSubmit() {
 }
 .form-title {
   font-family: "Brygada 1918", serif;
-  font-size: 15px;
+  font-size: 16px;
   font-weight: 500;
   color: var(--text-bright);
 }
@@ -183,7 +183,7 @@ function handleSubmit() {
   color: var(--text-faint);
   text-transform: none;
   letter-spacing: 0;
-  font-size: 9px;
+  font-size: 10px;
   margin-left: 4px;
   opacity: 0.7;
 }