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/models/assistant/function/create_goal_test.rb

@@ -1,16 +1,16 @@
 require "test_helper"
 
-class Assistant::Function::CreateSavingsGoalTest < ActiveSupport::TestCase
+class Assistant::Function::CreateGoalTest < ActiveSupport::TestCase
   setup do
     @user = users(:family_admin)
     @family = @user.family
     @depository = accounts(:depository)
-    @fn = Assistant::Function::CreateSavingsGoal.new(@user)
+    @fn = Assistant::Function::CreateGoal.new(@user)
   end
 
   test "to_definition returns valid JSON shape" do
     definition = @fn.to_definition
-    assert_equal "create_savings_goal", definition[:name]
+    assert_equal "create_goal", definition[:name]
     assert_kind_of String, definition[:description]
     assert_equal "object", definition[:params_schema][:type]
     assert_includes definition[:params_schema][:required], "name"
@@ -19,8 +19,8 @@ class Assistant::Function::CreateSavingsGoalTest < ActiveSupport::TestCase
   end
 
   test "creates a goal with linked accounts" do
-    assert_difference -> { SavingsGoal.count } => 1,
-                      -> { SavingsGoalAccount.count } => 1 do
+    assert_difference -> { Goal.count } => 1,
+                      -> { GoalAccount.count } => 1 do
       result = @fn.call(
         "name" => "Vacation",
         "target_amount" => 1500,
@@ -36,7 +36,7 @@ class Assistant::Function::CreateSavingsGoalTest < ActiveSupport::TestCase
   end
 
   test "creates a goal with initial contribution" do
-    assert_difference -> { SavingsContribution.count } => 1 do
+    assert_difference -> { GoalContribution.count } => 1 do
       @fn.call(
         "name" => "Laptop fund",
         "target_amount" => 2000,
@@ -45,7 +45,7 @@ class Assistant::Function::CreateSavingsGoalTest < ActiveSupport::TestCase
       )
     end
 
-    contribution = SavingsContribution.order(created_at: :desc).first
+    contribution = GoalContribution.order(created_at: :desc).first
     assert_equal "initial", contribution.source
     assert_equal 200, contribution.amount.to_i
   end