feat: Grafana copy publishing, dashboard examples, and optional OTel metrics

Implements three observability improvements:

#82 — publish_grafana_copy(): Uses SQLite online backup API (WAL-safe) to
atomically publish a consistent read-only copy beside the target. Adds
--publish-copy option to grafana-schema and snapshot CLI commands.

#83 — examples/grafana/: Minimal working Grafana setup with docker-compose,
provisioning datasource/dashboard YAML, and three dashboard JSON files
(mt5cli-overview, mt5cli-trades, mt5cli-market). All queries use grafana_*
views; no credentials or private paths included.

#84 — mt5cli/telemetry.py: Optional OTel metrics behind mt5cli[otel] extra.
Base install is unaffected. Adds _Mt5Metrics singleton (no-op until
configure_metrics() is called), wraps update_history() and
update_observability() with record_history_update / record_snapshot_update
context managers, and emits account/position gauges from snapshots.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/grafana/README.md

@@ -0,0 +1,87 @@
+# Grafana Integration for mt5cli
+
+This directory contains example configuration and dashboard files for visualising
+mt5cli SQLite data in [Grafana](https://grafana.com/) using the
+[Grafana SQLite datasource plugin](https://grafana.com/grafana/plugins/frser-sqlite-datasource/).
+
+## Prerequisites
+
+- mt5cli installed and able to connect to MetaTrader 5
+- Grafana 10+ with the `frser-sqlite-datasource` plugin installed
+- (Optional) Docker and Docker Compose for the containerised setup
+
+## Generating the SQLite database
+
+Collect historical data and snapshot current account state:
+
+```sh
+# Collect OHLCV history
+mt5cli -o history.db collect-history --symbol EURUSD --date-from 2024-01-01 --date-to 2024-12-31
+
+# Create Grafana-ready views and indexes
+mt5cli -o history.db grafana-schema
+
+# Snapshot current account, positions, and orders
+mt5cli -o history.db snapshot --with-grafana-schema
+```
+
+## Publishing a Grafana-readable copy
+
+Grafana reads the SQLite file directly. To avoid read/write conflicts, publish
+a consistent copy after each update:
+
+```sh
+mt5cli -o history.db grafana-schema --publish-copy history.grafana.db
+mt5cli -o history.db snapshot --publish-copy history.grafana.db
+```
+
+The `--publish-copy` option uses the SQLite online backup API, which is safe
+even when the source database uses WAL journal mode.
+
+## Configuring the datasource path
+
+Edit `provisioning/datasources/mt5cli-sqlite.yaml` and set the `path` field
+to the absolute path of your published `.db` file:
+
+```yaml
+jsonData:
+  path: /absolute/path/to/history.grafana.db
+```
+
+## Running Grafana on Windows (native)
+
+1. Download and install Grafana from <https://grafana.com/grafana/download/>.
+2. Install the SQLite plugin: `grafana-cli plugins install frser-sqlite-datasource`.
+3. Copy `provisioning/` into `%ProgramFiles%\GrafanaLabs\grafana\conf\provisioning\`.
+4. Import the dashboards from `dashboards/` via the Grafana UI
+   (Dashboards → Import → Upload JSON file).
+
+## Running with Docker Compose
+
+```sh
+# From the examples/grafana directory
+docker compose up -d
+```
+
+Then open <http://localhost:3000> (default credentials: admin / admin).
+
+The Compose file mounts this directory and the SQLite file into the container.
+Edit `docker-compose.yml` to point `MT5CLI_DB_PATH` at your `.db` file.
+
+## Dashboard overview
+
+| Dashboard | Description |
+|---|---|
+| `mt5cli-overview.json` | Account balance, equity, margin, and snapshot freshness |
+| `mt5cli-trades.json` | Trade P/L, win rate, symbol breakdown |
+| `mt5cli-market.json` | OHLCV rates, spreads, and tick volume |
+
+All panel queries use the `grafana_*` views; they do not read internal storage
+tables directly.
+
+## Importing dashboards
+
+1. Open Grafana and navigate to **Dashboards → Import**.
+2. Click **Upload JSON file** and select one of the files in `dashboards/`.
+3. Select the `mt5cli-SQLite` datasource when prompted.
+4. Click **Import**.