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.

app/components/goals/progress_ring_component.rb

@@ -0,0 +1,31 @@
+class Goals::ProgressRingComponent < ApplicationComponent
+  def initialize(goal:, size: 180)
+    @goal = goal
+    @size = size
+  end
+
+  attr_reader :goal, :size
+
+  def percent
+    goal.progress_percent
+  end
+
+  def amount_label
+    goal.current_balance_money.format
+  end
+
+  def target_label
+    goal.target_amount_money.format
+  end
+
+  def remaining_label
+    goal.remaining_amount_money.format
+  end
+
+  def percent_text_class
+    case goal.status
+    when :reached then "text-success"
+    else "text-primary"
+    end
+  end
+end