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>

app/controllers/api/v1/budgets_controller.rb

@@ -42,6 +42,16 @@ class Api::V1::BudgetsController < Api::V1::BaseController
     end
 
     def budgets_scope
-      current_resource_owner.family.budgets.includes(budget_categories: :category)
+      current_resource_owner.family.budgets
+        .where(user_id: visible_owner_ids)
+        .includes(budget_categories: :category)
+    end
+
+    # nil (the shared household budget) + the caller's own personal budget +
+    # any owner who granted the caller a BudgetShare (read-only or
+    # read-write — this API is read-only either way).
+    def visible_owner_ids
+      shared_with_me = BudgetShare.where(viewer_id: current_resource_owner.id).pluck(:owner_id)
+      [ nil, current_resource_owner.id, *shared_with_me ]
     end
 end