Add kids news channel; document per-source language filter

- New kids channel (/kids) with theme color, surfaced in the web UI
  and routed to by BBC Newsround, DOGO News, Science News Explores,
  and NASA for Students in the example config.
- README and config.example.toml now mention the optional
  per-source `language` filter added in the previous commit.

README.md

@@ -29,6 +29,7 @@ A Matrix news bot that ingests RSS feeds from curated sources and routes each st
 | `music` | Records, scenes, artists |
 | `anime` | Series, studios, manga |
 | `foss` | Kernel, distros, free/open source |
+| `kids` | World news written for younger readers (web-only) |
 
 ## Requirements
 
@@ -66,14 +67,14 @@ See `config.example.toml` for the full structure. Key sections:
 - `matrix` — homeserver, credentials, channel room IDs, optional admin room
 - `posting` — rate limiting (min interval, burst cap, daily cap), optional `round_robin` block
 - `storage` — database path, retention windows
-- `sources` — RSS feeds with tier, polling interval, and **required** `direct_route` (must match a key in `matrix.channels`)
+- `sources` — RSS feeds with tier, polling interval, and **required** `direct_route` (must match a key in `matrix.channels`). Optional `language = "en"` drops items whose per-item `<language>` tag doesn't prefix-match — handy for multilingual feeds like Politico Europe
 - `web` — read-only HTTP UI (enabled toggle, listen address, site title, public base URL)
 
 Environment variables can be referenced with `${VAR}` syntax in the TOML.
 
 ### Web UI
 
-Set `web.enabled: true` (default port `:8080`) to expose Pete's classified-story archive over HTTP. A landing page at `/` plus one section per channel (`/gaming`, `/tech`, `/politics`, `/eu`, `/music`, `/anime`, `/foss`), all pulling from the `stories` table. A `/weather` page demos the seasonal canvas overlay in isolation. Adding a section is two lines in `internal/web/server.go` (the `channels` slice) plus a matching theme color in `internal/web/static/css/input.css`.
+Set `web.enabled: true` (default port `:8080`) to expose Pete's classified-story archive over HTTP. A landing page at `/` plus one section per channel (`/gaming`, `/tech`, `/politics`, `/eu`, `/music`, `/anime`, `/foss`, `/kids`), all pulling from the `stories` table. A `/weather` page demos the seasonal canvas overlay in isolation. Adding a section is two lines in `internal/web/server.go` (the `channels` slice) plus a matching theme color in `internal/web/static/css/input.css`.
 
 The frontend uses a small Tailwind build: