Add jail distribution chart (Stage 5)

- backend: GET /api/dashboard/bans/by-jail endpoint
  - JailBanCount + BansByJailResponse Pydantic models in ban.py
  - bans_by_jail() service function with origin filter support
  - Route added to dashboard router
  - 17 new tests (7 service, 10 router); full suite 497 passed, 83% coverage

- frontend: JailDistributionChart component
  - JailBanCount / BansByJailResponse types in types/ban.ts
  - dashboardBansByJail endpoint constant in api/endpoints.ts
  - fetchBansByJail() in api/dashboard.ts
  - useJailDistribution hook in hooks/useJailDistribution.ts
  - JailDistributionChart component (horizontal bar chart, Recharts)
  - DashboardPage: full-width Jail Distribution section below Top Countries

Docs/Tasks.md

@@ -353,7 +353,15 @@ Add the `BanTrendChart` to the dashboard page **above** the two country charts a
 
 ### Task 5.1 — Add a backend endpoint for ban counts per jail
 
-**Status:** `not started`
+**Status:** `done`
+
+Added `GET /api/dashboard/bans/by-jail`. New Pydantic models `JailBanCount` and
+`BansByJailResponse` added to `ban.py`. Service function `bans_by_jail()` in
+`ban_service.py` queries the `bans` table with `GROUP BY jail ORDER BY COUNT(*) DESC`
+and applies the origin filter. Route added to `dashboard.py`. 7 new service tests
+(happy path, total equality, empty DB, time-window exclusion, origin filter variants)
+and 10 new router tests — all pass, total suite 497 passed, 83% coverage.
+`ruff check` and `mypy --strict` pass.
 
 The existing `GET /api/jails` endpoint returns jail metadata with `status.currently_banned` — but this counts **currently active** bans, not historical bans in the selected time window. The dashboard needs historical ban counts per jail within the selected time range.
 
@@ -395,7 +403,16 @@ class BansByJailResponse(BaseModel):
 
 ### Task 5.2 — Create the `JailDistributionChart` component
 
-**Status:** `not started`
+**Status:** `done`
+
+Created `frontend/src/components/JailDistributionChart.tsx` — a horizontal
+bar chart using Recharts `BarChart` showing ban counts per jail sorted descending.
+Added `JailBanCount`/`BansByJailResponse` types to `types/ban.ts`,
+`dashboardBansByJail` constant to `api/endpoints.ts`, `fetchBansByJail()` to
+`api/dashboard.ts`, and the `useJailDistribution` hook at
+`hooks/useJailDistribution.ts`. Component handles loading (Spinner), error
+(MessageBar), and empty states inline. `tsc --noEmit` and ESLint pass with zero
+warnings.
 
 Create `frontend/src/components/JailDistributionChart.tsx`. This component renders a **horizontal bar chart** showing the distribution of bans across jails.
 
@@ -422,7 +439,14 @@ Create `frontend/src/components/JailDistributionChart.tsx`. This component rende
 
 ### Task 5.3 — Integrate the jail distribution chart into `DashboardPage`
 
-**Status:** `not started`
+**Status:** `done`
+
+Added a full-width "Jail Distribution" section card to `DashboardPage` below the
+"Top Countries" section (2-column country charts on row 1, jail chart full-width
+on row 2). The section renders `<JailDistributionChart timeRange={timeRange}
+origin={originFilter} />`, sharing the same state already used by the other
+charts. Loading, error, and empty states are handled inside
+`JailDistributionChart` itself. `tsc --noEmit` and ESLint pass with zero warnings.
 
 Add the `JailDistributionChart` as a third chart card alongside the two country charts, or in a second chart row below them if space is constrained.