feat(server): add OpenNest.Server SQLite nest storage API

SQLite-backed (Microsoft.Data.Sqlite, WAL) minimal API storing NestRecord
metadata plus the .nest archive as a BLOB. Endpoints: GET/POST /api/nests,
GET /api/nests/{id}[/file], PUT /api/nests/{id}/file, PUT
/api/nests/{id}/metadata, DELETE /api/nests/{id}, GET /healthz. Multipart
upload contract matches RemoteNestRepository (metadata JSON part + file
part). Added to OpenNest.sln, builds standalone on Linux. Dockerfile
publishes to a runtime image listening on :8090 with a /app/data volume
for the SQLite file. docs/nest-storage.md documents the wire contract,
endpoints and deployment.

Full curl round trip verified manually against a running instance:
upload (server-assigned id + computed fileSize), list, get, byte-exact
file download, metadata-only update (archive unchanged), file update
(new archive persisted), 404s for unknown ids, delete, post-delete 404.

docs/nest-storage.md

@@ -0,0 +1,84 @@
+# Nest storage: File mode vs. Database mode
+
+The desktop app can save nests two ways:
+
+- **File mode** (default, unchanged behavior): Save/Save As write a `.nest` ZIP
+  archive to disk via the normal file dialog. See [nest-file-format.md](nest-file-format.md).
+- **Database mode**: Save uploads the nest to a central `OpenNest.Server`
+  instance shared by every shop PC, instead of writing a local file. A separate
+  **File > Export .nest...** command is always available (in both modes) for
+  producing a local file to share or back up.
+
+The mode and server address are stored per-PC at `%APPDATA%\OpenNest\storage.json`
+(`OpenNest.Data.NestStorageSettings`), defaulting to File mode so existing
+installs are unaffected until an operator opts in via **File > Storage Mode...**.
+
+## Wire contract
+
+`OpenNest.Data.NestRecord` is the metadata DTO shared by the client
+(`RemoteNestRepository`) and the server (`OpenNest.Server`). JSON is camelCase
+with enums serialized as strings (`JsonSerializerDefaults.Web` +
+`JsonStringEnumConverter(JsonNamingPolicy.CamelCase)`), matching the rest of
+`OpenNest.Data`'s local JSON stores.
+
+| Field | Type | Notes |
+|---|---|---|
+| `id` | guid | Client-generated on first save; kept on updates. |
+| `name` | string | |
+| `customer` | string | |
+| `dateCreated` / `dateModified` | datetime | Set by the client from the nest's own metadata. |
+| `material` | string | |
+| `thickness` | number | |
+| `status` | `"quote"` \| `"toBeCut"` \| `"hasBeenCut"` | Default `quote`. |
+| `plateCount` / `partCount` | integer | Computed client-side at save time (non-cutoff parts only). |
+| `comments` | string | |
+| `madeBy` | string | |
+| `fileSize` | integer | Server-computed; ignored on upload. |
+| `savedAt` | datetime | Server-computed; ignored on upload. |
+
+## Endpoints
+
+| Method | Path | Body | Response |
+|---|---|---|---|
+| GET | `/healthz` | — | `{ "status": "ok" }` |
+| GET | `/api/nests` | — | `NestRecord[]`, newest `savedAt` first |
+| GET | `/api/nests/{id}` | — | `NestRecord` or 404 |
+| GET | `/api/nests/{id}/file` | — | `.nest` archive bytes (`application/zip`) or 404 |
+| POST | `/api/nests` | multipart: `metadata` (JSON `NestRecord`) + `file` (`.nest` bytes) | `NestRecord` with server-assigned `id` when the client sends an empty guid |
+| PUT | `/api/nests/{id}/file` | multipart: `metadata` + `file` | Updated `NestRecord`, or 404 if `id` is unknown |
+| PUT | `/api/nests/{id}/metadata` | JSON `NestRecord` | Updated `NestRecord` (archive untouched), or 404 |
+| DELETE | `/api/nests/{id}` | — | 204, or 404 |
+
+There is no authentication; this is a LAN-only service. Do not expose it
+outside the shop network without adding one.
+
+## Storage
+
+`OpenNest.Server.NestDatabase` uses SQLite (`Microsoft.Data.Sqlite`) with
+`journal_mode=WAL`. Each row holds the metadata columns plus the `.nest`
+archive as a `BLOB`. The database file path comes from `--database=<path>`,
+then `OPENNEST_DB`, defaulting to `./data/nests.db`.
+
+## Running
+
+Locally:
+
+```sh
+dotnet run --project OpenNest.Server/OpenNest.Server.csproj
+```
+
+Listens on `ASPNETCORE_URLS` (default Kestrel ports) unless overridden.
+
+Docker (built from the repository root so it can see `OpenNest.Data`):
+
+```sh
+docker build -f OpenNest.Server/Dockerfile -t opennest-server .
+docker run -d -p 8090:8090 -v opennest-data:/app/data opennest-server
+```
+
+The image listens on `:8090` and stores `nests.db` under `/app/data`, which
+should be a named volume or bind mount so nests survive container recreation.
+
+Point the desktop app's **File > Storage Mode...** server URL at
+`http://<host>:8090` (no trailing slash required; `RemoteNestRepository`
+trims it).