feat(budgets): add per-user personal budgets with strict isolation (#2891)

* feat(budgets): add per-user personal budgets with strict isolation

Families can now opt into personal budgets (toggleable via family
settings): each family member gets their own budget for a given
period instead of sharing a single family-wide budget.

- Add families.personal_budgets flag and budgets.user_id, with
  partial unique indexes so shared budgets (user_id IS NULL) and
  personal budgets (user_id IS NOT NULL) can't collide.
- Budget.find_or_bootstrap scopes lookup/creation by user when the
  family has personal_budgets enabled.
- Scope most_recent_initialized_budget (used to seed a new budget
  from the prior period) by user_id so one user's copy-forward never
  bleeds into another user's budget.
- budgets.user_id cascades on user deletion so personal budgets don't
  outlive their owner.

* feat(budgets): enforce user-specific budget ownership and cascade deletion

* feat(budgets): display user name for personal budgets in budget card on the plan section

* feat(budgets): enhance personal budgets display for admins with preview feature indication

* feat(budgets): enforce user-specific budget and category visibility for personal budgets

* feat(budgets): create budget section titles and add translations notice in preferences

* feat(budgets): let household and personal budgets coexist with sharing

Previously enabling personal_budgets made the shared household budget
unreachable. Budget.find_or_bootstrap now takes an explicit household:
flag so both can be resolved independently for the same period, with a
new household_budget_enabled family setting to opt out of the household
side and keep personal budgets only.

Adds a BudgetShare model (read_only/read_write) so a member can grant
another family member access to their personal budget, enforced via
Budget#viewable_by?/editable_by? across BudgetsController,
BudgetCategoriesController, PlansController, and the read-only API.
Preferences gains a Budget sharing card (gated on preview access like
the rest of the personal budgets UI) and an owner switcher pill (
Household / mine / shared-with-me) appears on the budget page and the
Plan hub card.

Also fixes personal budgets showing the same "actual spending" as the
household budget: actual spending/income now scope to the budget
owner's own accounts instead of the viewer's full accessible set,
via a new accounts: override on IncomeStatement.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* feat(budgets): enhance budget switcher with icons and improved styling

* feat(budgets): remove user name display from budget card and header

* feat(budgets): remove unique index on taggable_type and taggable_id in taggings

* feat(budgets): enhance budget sharing functionality and improve UI elements

* Collapse personal budget migrations

---------

Signed-off-by: JulienGourmet <69808509+jubbakka@users.noreply.github.com>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
Co-authored-by: sure-admin <sure-admin@splashblot.com>

test/controllers/api/v1/budgets_controller_test.rb

@@ -116,6 +116,47 @@ class Api::V1::BudgetsControllerTest < ActionDispatch::IntegrationTest
     assert_equal "validation_failed", response_data["error"]
   end
 
+  test "excludes another family member's personal budget" do
+    @family.update!(personal_budgets: true)
+
+    other_member_budget = @family.budgets.create!(
+      user: users(:family_member),
+      start_date: 5.months.ago.beginning_of_month.to_date,
+      end_date: 5.months.ago.end_of_month.to_date,
+      budgeted_spending: 800,
+      currency: "USD"
+    )
+
+    get api_v1_budgets_url, headers: api_headers(@api_key)
+    assert_response :success
+    response_data = JSON.parse(response.body)
+    assert_not_includes response_data["budgets"].map { |budget| budget["id"] }, other_member_budget.id
+
+    get api_v1_budget_url(other_member_budget.id), headers: api_headers(@api_key)
+    assert_response :not_found
+  end
+
+  test "includes another family member's personal budget once they share it" do
+    @family.update!(personal_budgets: true)
+
+    other_member_budget = @family.budgets.create!(
+      user: users(:family_member),
+      start_date: 5.months.ago.beginning_of_month.to_date,
+      end_date: 5.months.ago.end_of_month.to_date,
+      budgeted_spending: 800,
+      currency: "USD"
+    )
+    BudgetShare.create!(owner: users(:family_member), viewer: @user, permission: "read_only")
+
+    get api_v1_budgets_url, headers: api_headers(@api_key)
+    assert_response :success
+    response_data = JSON.parse(response.body)
+    assert_includes response_data["budgets"].map { |budget| budget["id"] }, other_member_budget.id
+
+    get api_v1_budget_url(other_member_budget.id), headers: api_headers(@api_key)
+    assert_response :success
+  end
+
   test "requires authentication" do
     get api_v1_budgets_url