web: delete a category and report how many subscriptions were uncategorised #224

Parent

#196 — PRD: Angular web client for SubVora (parity minus reminders)

What to build

Deleting a user's own category. Subscriptions using it are not deleted — they become uncategorised, because losing a grouping beats losing the record — and the API reports how many were affected. The dialog must state that consequence before the fact, and the app must report the count afterwards.

Implementation Steps

1. API method — add remove(id) to core/api/categories-api.service.ts returning { subscriptionsUncategorized } on 200, 404 for a system default or another user's category.
2. Consequence dialog — reuse shared/confirm-dialog.component.ts (from the subscription delete slice) with copy that names the category and states plainly that its subscriptions will become uncategorised, not deleted.
3. Store method — remove(id) in categories.store.ts drops the item on success and returns the count; a 404 reports "Not found." and reloads.
4. Report and propagate — show "N subscriptions are now uncategorised" (correctly singular for one, and a plain confirmation for zero), then refresh the subscriptions list store if loaded so those rows move to the uncategorised group.
5. Spec — categories.store.spec.ts additions: a successful delete removes the item and reports the returned count; zero affected still confirms; the subscriptions store is refreshed only when it holds data.

Agent Routing

agent_routing:
  complexity_hint: easy
  required_capability: balanced
  parallel_safe: true
  cost_preference: low
  speed_preference: balanced
  ownership_scope:
    - src/SubVora.Web/src/app/features/categories/**
    - src/SubVora.Web/src/app/core/api/categories-api.service.ts
  verification:
    - cd src/SubVora.Web && npx ng test --no-watch

Technical Context Snapshot

Current stack in scope

• UI: Angular (20+) standalone components with signals and built-in control flow, Angular Material (Material 3) as the only component library, SCSS. Static SPA — no SSR, no service worker.
• State: signal-backed injectable stores, one per domain area, mirroring the MAUI ViewModel split in src/SubVora.Mobile/ViewModels one-to-one. No NgRx.
• API access: hand-written models plus one service per API controller under src/SubVora.Web/src/app/core/api. Enums travel as JSON strings (JsonStringEnumConverter in Program.cs), so TypeScript string-literal unions are exact.
• Backend consumed unchanged: ASP.NET Core net10.0, /api/v1/, JWT bearer in the Authorization header, tokens in JSON bodies (no cookies).
• Tests: Angular CLI unit-test builder (Vitest runner; Karma is deprecated) with HttpTestingController. Stores, interceptors, mappers and utils only — no component-DOM or browser automation.

Dependencies in scope

• Reuse: @angular/*, @angular/material, rxjs, and the utilities already added under src/SubVora.Web/src/app/core. No chart library, no date library, no HTTP wrapper library.
• New dependency additions allowed for this slice: no. If a dependency looks unavoidable, stop and raise it on the issue rather than adding it.

Architecture alignment

• Preserve the repo's load-bearing rules (CLAUDE.md): burn-rate maths is server-side and counts cycles, never days; currency conversion is a read-time projection and stored amounts are never overwritten; nothing advances next_billing_date on a timer; provider matching stays one SQL query; the mobile SQLite cache stays a read-only mirror.
• There is deliberately no shared DTO project. Web models mirror the API's JSON contract by convention — a contract change means editing both sides.
• create-git-issue provides routing hints only and assigns no concrete agent or model.
• run-with-it remains the final runtime routing authority.

Integration touchpoints

• Consumes DELETE /api/v1/categories/{id} returning DeleteCategoryResult { subscriptionsUncategorized }.
• Server behaviour: subscriptions are uncategorised rather than deleted, and system defaults answer 404.
• The subscriptions list groups by category name, so affected rows must move to the uncategorised group after a delete.

Acceptance criteria

• The confirmation states that subscriptions will become uncategorised rather than deleted.
• After deleting, the affected count is reported and those subscriptions appear in the uncategorised group.
• System default categories offer no delete action.

Blocked by

• web: categories screen with inline create #222 (slice 26)