fix(goals): drop new-goal stepper, unify create + edit form

The 2-step stepper on the create modal carried a review step whose only
real signal was a derived "Save $X/mo to hit it on time" hint. Name,
amount, and date are all visible in step 1, so the review step was
re-displaying form values the user just typed.

Collapses both flows into a single panel:

- `_form_stepper.html.erb` + `_form_edit.html.erb` → single
  `_form.html.erb` driven by `goal.persisted?` for URL / method /
  submit label.
- `goal_stepper_controller.js` → `goal_form_controller.js`. Drops the
  step1Panel / step2Panel / step1Indicator / step2Indicator /
  step1Circle / step2Circle / stepperLine / reviewName / reviewSummary
  / reviewSuggested / footerLeftButton / footerRightButton / submitButton
  target plumbing and the next / back / blockEnter / updateStepperState
  / updateFooter / updateReview methods. Keeps name-validation,
  amount-validation, accounts-required validation, avatar-preview-from-
  name, and the suggested-pace computation — that one now writes into
  an inline `<p data-goal-form-target="suggested">` below the
  target_date field instead of the review card.
- `new.html.erb`: drops the `Step 1 of 2 · Goal details` subtitle
  target. New `goals.new.subtitle` replaces the two step subtitles.
- `edit.html.erb`: renders the same `form` partial.
- `_color_picker.html.erb`: `data-goal-stepper-target="avatarPreview"`
  → `data-goal-form-target="avatarPreview"` (same Stimulus target,
  renamed for the new controller scope).
- `funding_accounts_breakdown_component.rb`: i18n key path moves to
  `goals.form.subtypes.*` matching the locale restructure.
- `en.yml`: `goals.form_stepper.step1.fields.*` → `goals.form.fields.*`.
  `step2.*` and the `back` / `continue` / `cancel` keys drop. New
  `goals.form.create` ("Create goal") + `goals.form.save` ("Save
  changes") drive the submit-button label.

UX delta: the user no longer sees a "Step 1 of 2 / Step 2 of 2" beat.
The form is short enough that everything fits in one panel; the only
value-add from the old step 2 — the suggested-pace hint — now updates
live inline as the amount / date / account-count changes.

All 20 `test/controllers/goals_controller_test.rb` tests still pass.
`bundle exec erb_lint` clean on the touched templates.

app/javascript/controllers/goal_form_controller.js

@@ -0,0 +1,141 @@
+import { Controller } from "@hotwired/stimulus";
+
+// Single-form controller for the goal create / edit modal.
+//
+// Replaces the 2-step stepper: the form is short enough that all fields
+// fit on one panel, so the previous review step (which only showed a
+// derived "Save $X/mo to hit it on time" hint) collapses into an inline
+// live hint below the target date. Validation + avatar preview from the
+// name field still live here.
+export default class extends Controller {
+  static targets = [
+    "nameInput",
+    "amountInput",
+    "dateInput",
+    "avatarPreview",
+    "nameError",
+    "amountError",
+    "accountsError",
+    "linkedAccountCheckbox",
+    "suggested",
+  ];
+
+  static INVALID_INPUT_CLASSES = ["ring-2", "ring-destructive", "border-destructive"];
+
+  static values = {
+    currency: { type: String, default: "USD" },
+    suggestedWithDate: { type: String, default: "Save {monthly}/mo across {accounts} to hit it on time." },
+    suggestedNoDate: { type: String, default: "Set a target date to project a finish line." },
+  };
+
+  connect() {
+    // Capture the default avatar contents (the "target" icon SVG) so we
+    // can restore it when the user clears the name field after typing.
+    if (this.hasAvatarPreviewTarget) {
+      this._defaultAvatarHTML = this.avatarPreviewTarget.innerHTML;
+    }
+    this.updateSuggested();
+  }
+
+  nameChanged() {
+    if (this.hasNameInputTarget) {
+      this.clearFieldError(this.nameInputTarget, this.hasNameErrorTarget ? this.nameErrorTarget : null);
+    }
+    if (!this.hasAvatarPreviewTarget || !this.hasNameInputTarget) return;
+
+    // If the user has explicitly picked an icon, leave it alone. Name
+    // changes shouldn't undo an explicit choice.
+    const iconPicked = this.element.querySelector('input[name="goal[icon]"]:checked');
+    if (iconPicked) return;
+
+    const name = this.nameInputTarget.value.trim();
+    if (name) {
+      this.avatarPreviewTarget.textContent = name.charAt(0).toUpperCase();
+    } else if (this._defaultAvatarHTML) {
+      // Captured at connect. Restore the default "target" icon from the
+      // server-rendered template, not a "?" character.
+      this.avatarPreviewTarget.innerHTML = this._defaultAvatarHTML;
+    }
+  }
+
+  amountChanged() {
+    if (this.hasAmountInputTarget) {
+      this.clearFieldError(this.amountInputTarget, this.hasAmountErrorTarget ? this.amountErrorTarget : null);
+    }
+  }
+
+  linkedAccountChanged() {
+    this.updateSuggested();
+    if (this.linkedAccountCheckboxTargets.some((cb) => cb.checked) && this.hasAccountsErrorTarget) {
+      this.accountsErrorTarget.classList.add("hidden");
+    }
+  }
+
+  // Hook for any input that influences the suggested-pace hint
+  // (target_amount, target_date). Also re-evaluates as accounts toggle.
+  suggestedChanged() {
+    this.amountChanged();
+    this.updateSuggested();
+  }
+
+  updateSuggested() {
+    if (!this.hasSuggestedTarget) return;
+
+    const amount = this.hasAmountInputTarget ? Number.parseFloat(this.amountInputTarget.value) : NaN;
+    const dateValue = this.hasDateInputTarget ? this.dateInputTarget.value : null;
+    const checkedCount = this.linkedAccountCheckboxTargets.filter((cb) => cb.checked).length;
+
+    const amountValid = Number.isFinite(amount) && amount > 0;
+    if (!amountValid || checkedCount === 0) {
+      this.suggestedTarget.classList.add("hidden");
+      this.suggestedTarget.textContent = "";
+      return;
+    }
+
+    let text;
+    if (dateValue) {
+      const months = this.#monthsBetween(new Date(), new Date(dateValue));
+      if (months <= 0) {
+        this.suggestedTarget.classList.add("hidden");
+        this.suggestedTarget.textContent = "";
+        return;
+      }
+      const perMonth = Math.ceil(amount / months);
+      const accountLabel = `${checkedCount} ${checkedCount === 1 ? "account" : "accounts"}`;
+      text = this.suggestedWithDateValue
+        .replace("{monthly}", this.#money(perMonth))
+        .replace("{accounts}", accountLabel);
+    } else {
+      text = this.suggestedNoDateValue;
+    }
+
+    this.suggestedTarget.textContent = text;
+    this.suggestedTarget.classList.remove("hidden");
+  }
+
+  showFieldError(input, errorEl) {
+    if (input) input.classList.add(...this.constructor.INVALID_INPUT_CLASSES);
+    if (errorEl) errorEl.classList.remove("hidden");
+  }
+
+  clearFieldError(input, errorEl) {
+    if (input) input.classList.remove(...this.constructor.INVALID_INPUT_CLASSES);
+    if (errorEl) errorEl.classList.add("hidden");
+  }
+
+  #money(value) {
+    try {
+      return new Intl.NumberFormat(undefined, {
+        style: "currency",
+        currency: this.currencyValue || "USD",
+        maximumFractionDigits: 0,
+      }).format(value);
+    } catch {
+      return `${this.currencyValue || "$"}${Math.round(value).toLocaleString()}`;
+    }
+  }
+
+  #monthsBetween(from, to) {
+    return (to - from) / (1000 * 60 * 60 * 24 * 30.44);
+  }
+}