refactor: rename Savings Goals feature to Goals

User-facing rename + structural rename. Feature is now called just
"Goals" everywhere — page title, sidebar nav, modal headings, flash
messages, AI assistant tool. Code identifiers follow:

- Models: SavingsGoal → Goal, SavingsContribution → GoalContribution,
  SavingsGoalAccount → GoalAccount.
- Tables: savings_goals → goals, savings_contributions → goal_contributions,
  savings_goal_accounts → goal_accounts. FK columns savings_goal_id →
  goal_id. New migration db/migrate/20260511100003_rename_savings_to_goals.rb
  uses rename_table + rename_column; PG handles index renaming and FK
  redirection automatically.
- Controllers: SavingsGoalsController → GoalsController,
  SavingsContributionsController → GoalContributionsController.
- Routes: /savings_goals → /goals, nested /goals/:id/contributions
  (resource name shifts; old route name aliases dropped).
- ViewComponent namespace: Savings::* → Goals::*. Component class
  names drop their redundant "Goal" prefix where the namespace already
  carries it: Savings::GoalCardComponent → Goals::CardComponent,
  Savings::GoalAvatarComponent → Goals::AvatarComponent. Others keep
  their names (Goals::ProgressRingComponent, Goals::StatusPillComponent,
  Goals::AccountStackComponent, Goals::FundingAccountsBreakdownComponent).
- Stimulus controllers: savings_goal_* → goal_*, savings_goals_filter
  → goals_filter. Stimulus identifiers in data-controller / data-*
  attributes follow.
- Locale keys: savings_goals: → goals: (top level), savings_contributions:
  → goal_contributions: (top level). All t() callers updated.
- AI assistant tool: Assistant::Function::CreateSavingsGoal →
  Assistant::Function::CreateGoal, tool name "create_savings_goal" →
  "create_goal", description / response text updated.
- Sidebar nav label "Savings" → "Goals". Goals/show + index page title
  "Savings" → "Goals". Empty goals_section heading/subtitle dropped
  (duplicated the page title post-rename).

Original migrations create_savings_goals / create_savings_goal_accounts /
create_savings_contributions remain untouched so historical replay
still works; the rename migration runs on top.

test/controllers/goal_contributions_controller_test.rb

@@ -0,0 +1,58 @@
+require "test_helper"
+
+class GoalContributionsControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    sign_in users(:family_admin)
+    @goal = goals(:vacation_italy)
+    @depository = accounts(:depository)
+    ensure_tailwind_build
+  end
+
+  test "new renders the modal form" do
+    get new_goal_contribution_url(@goal)
+    assert_response :success
+  end
+
+  test "create saves a manual contribution" do
+    assert_difference -> { @goal.goal_contributions.count } => 1 do
+      post goal_contributions_url(@goal), params: {
+        goal_contribution: {
+          amount: "100",
+          contributed_at: Date.current.iso8601,
+          notes: ""
+        },
+        goal_contribution_account_id: @depository.id
+      }.merge(goal_contribution: { account_id: @depository.id, amount: "100", contributed_at: Date.current.iso8601 })
+    end
+
+    assert_redirected_to goal_path(@goal)
+    contribution = @goal.goal_contributions.order(created_at: :desc).first
+    assert_equal "manual", contribution.source
+    assert_equal @depository, contribution.account
+  end
+
+  test "create rejects contribution from non-linked account" do
+    unlinked = Account.create!(family: @goal.family, accountable: Depository.new, name: "Unlinked", currency: "USD", balance: 100)
+    assert_no_difference "@goal.goal_contributions.count" do
+      post goal_contributions_url(@goal), params: {
+        goal_contribution: { amount: "10", contributed_at: Date.current.iso8601, account_id: unlinked.id }
+      }
+    end
+    assert_response :unprocessable_entity
+  end
+
+  test "destroy manual contribution removes it" do
+    manual = goal_contributions(:vacation_italy_manual)
+    assert_difference "GoalContribution.count", -1 do
+      delete goal_contribution_url(@goal, manual)
+    end
+  end
+
+  test "destroy initial contribution is blocked" do
+    initial = goal_contributions(:vacation_italy_initial)
+    assert_no_difference "GoalContribution.count" do
+      delete goal_contribution_url(@goal, initial)
+    end
+    assert_redirected_to goal_path(@goal)
+  end
+end