Add events calendar with ICS feed and switch content naming to English

docs/inhalte-pflegen.md

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+# Editing content
+
+How to add or change the visitor-facing content of the site. All content lives
+as files under `Elternbeirat.Web/Content/` — there is no database and no admin
+interface. Every change needs a **commit** and a **rebuild** of the image, since
+the content ships inside the image, not in a volume.
+
+> **Language convention.** File and folder names, front-matter keys and YAML keys
+> are English (`posts/`, `title:`, `start:`). The text a visitor reads stays
+> German — that includes the *value* after a key (`title: Vorstandsteam`) and the
+> Markdown body. So you write English keys with German values.
+
+The three content kinds:
+
+| Kind | Where | New entry = |
+|---|---|---|
+| Page | `Content/pages/*.md` | one Markdown file |
+| Post (news) | `Content/posts/*.md` | one Markdown file |
+| Event (calendar) | `Content/events.yml` | one entry in the list |
+
+None of these touch a `.razor` file.
+
+---
+
+## Pages
+
+A page is a standalone Markdown file in `Content/pages/`. The file name (without
+`.md`) is the slug and therefore the URL: `vorstandsteam.md` is served at
+`/vorstandsteam`.
+
+Front matter at the top sets the title; the body is the content:
+
+```markdown
+---
+title: Vorstandsteam
+---
+
+# Vorstandsteam
+
+Hier stellt sich das Team vor …
+```
+
+- **Slugs have no umlauts.** Use `ueber-uns`, not `über-uns`; `foerderverein`,
+  not `förderverein`. The visible heading in the body may of course use umlauts.
+- If you omit `title:`, the slug is used as the title — so always set it.
+- Add the new page to the navigation only if it should appear there: edit
+  `Components/Layout/MainLayout.razor`. Pages that are only linked from other
+  pages (like the FAQ sub-pages) do not need a nav entry.
+
+---
+
+## Posts (news)
+
+A post is a Markdown file in `Content/posts/`, same idea as a page but with a
+date. Posts show up in the news list at `/beitraege`, newest first, and each has
+its own URL at `/beitraege/<slug>`.
+
+```markdown
+---
+title: Neue Sporthalle feierlich eröffnet
+date: 2025-10-05
+---
+
+# Neue Sporthalle feierlich eröffnet
+
+Der Text des Beitrags …
+```
+
+- `date:` is an ISO date, **`yyyy-MM-dd`**. It drives the sort order (newest
+  first) and the displayed date. A missing or malformed date sorts the post last
+  rather than breaking the build.
+- The three most recent posts are also teased on the home page automatically —
+  nothing to do there.
+
+---
+
+## Events (calendar)
+
+Events are **not** separate files. They all live in the single list
+`Content/events.yml`. Add an entry to the list:
+
+```yaml
+- title: Elternbeiratssitzung
+  start: "2026-10-08 19:30"
+  location: Lehrerzimmer
+  note: Themen bitte vorab per E-Mail einreichen.
+```
+
+Keys:
+
+| Key | Required | Meaning |
+|---|---|---|
+| `title` | yes | Short name shown in the list and calendar |
+| `start` | yes | When it starts — see date formats below |
+| `end` | no | End, for entries that span hours or days |
+| `location` | no | e.g. `Aula`, `Mensa` |
+| `note` | no | Free text shown below the entry |
+
+**Date formats** for `start` and `end`:
+
+- Date only → all-day event: `"2026-03-15"`
+- Date with time: `"2026-03-15 19:30"` (24-hour clock)
+
+Always keep the value in quotes so YAML treats it as text.
+
+The overview at `/termine` splits the list automatically: entries today or later
+appear under *Kommende Termine* (earliest first), past ones under *Vergangene
+Termine* (most recent first). You do not sort the file yourself — order in the
+YAML does not matter.
+
+Visitors can subscribe to `/termine.ics` in their own calendar app; that feed is
+generated from the same file, so a new entry appears there too.
+
+> A malformed `start` drops just that one entry instead of breaking the whole
+> page, so a typo in one event will not take the calendar down — but the entry
+> silently disappears. If an event does not show up, check its `start` value.
+
+---
+
+## Publishing a change
+
+A content change is not live until the image is rebuilt and redeployed:
+
+1. Edit or add the file under `Content/`.
+2. Check it locally with `dotnet run --project Elternbeirat.Web`. Content is read
+   once at startup, so after editing a file **restart the process** to see the
+   change (or use `dotnet watch` to restart on save automatically).
+3. Commit the change.
+4. Rebuild and redeploy the image — see [deployment](deployment.md).