feat(savings_goals/new): drop required asterisks, hide currency, collapse notes, clean footer

P1 of modal refactor — visual fidelity baseline against the Claude
Design reference and refactoring-ui rules.

Drop required: true on name + target_amount (suppresses both the red `*`
indicator and the browser-default HTML5 validation tooltip). Client-side
validation moves into the Stimulus stepper in a follow-up commit.

Pass hide_currency: true on the money_field so single-currency families
don't see a redundant inline currency dropdown.

Wrap the Notes textarea in a <details> disclosure ("Add notes (optional)"
summary) so step 1 isn't padded with rarely-used fields.

Drop the footer top border-subdued divider so the action row floats
against the dialog's existing padding boundary.

Drop the view-layer SavingsGoal::COLORS.sample fallback on hidden color
field — the controller already seeds @savings_goal.color.

config/locales/views/savings_goals/en.yml

@@ -196,6 +196,8 @@ en:
           target_date: Target date
           color: Color
           notes: Notes (optional)
+          notes_summary: Add notes (optional)
+          notes_placeholder: A reminder for future you…
           funding_accounts: Funding accounts
         subtypes:
           checking: Checking