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>

tests/test_examples.py

@@ -0,0 +1,75 @@
+"""Tests for example files in examples/grafana/."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+_EXAMPLES_DIR = Path(__file__).parent.parent / "examples" / "grafana"
+_DASHBOARDS_DIR = _EXAMPLES_DIR / "dashboards"
+
+
+class TestGrafanaExamples:
+    """Validate structure and content of bundled Grafana example files."""
+
+    def test_dashboard_json_files_are_valid_json(self) -> None:
+        """All dashboard JSON files parse without error."""
+        paths = list(_DASHBOARDS_DIR.glob("*.json"))
+        assert paths, "No dashboard JSON files found"
+        for path in paths:
+            content = path.read_text(encoding="utf-8")
+            obj = json.loads(content)
+            assert isinstance(obj, dict), f"{path.name} root must be a JSON object"
+
+    def test_dashboard_json_has_no_private_placeholders(self) -> None:
+        """Dashboard JSON files contain no obvious credential placeholders."""
+        private_patterns = ["password", "api_key", "apikey"]
+        for path in _DASHBOARDS_DIR.glob("*.json"):
+            content = path.read_text(encoding="utf-8").lower()
+            for pat in private_patterns:
+                assert pat not in content, f"{path.name} contains {pat!r}"
+
+    def test_dashboard_json_uses_grafana_views(self) -> None:
+        """All dashboard JSON files query grafana_* views."""
+        for path in _DASHBOARDS_DIR.glob("*.json"):
+            content = path.read_text(encoding="utf-8")
+            assert "grafana_" in content, (
+                f"{path.name} must contain queries against grafana_* views"
+            )
+
+    def test_dashboard_json_has_uid(self) -> None:
+        """All dashboard JSON files have a non-empty uid field."""
+        for path in _DASHBOARDS_DIR.glob("*.json"):
+            obj = json.loads(path.read_text(encoding="utf-8"))
+            assert obj.get("uid"), f"{path.name} must have a uid"
+
+    def test_dashboard_json_has_title(self) -> None:
+        """All dashboard JSON files have a non-empty title field."""
+        for path in _DASHBOARDS_DIR.glob("*.json"):
+            obj = json.loads(path.read_text(encoding="utf-8"))
+            assert obj.get("title"), f"{path.name} must have a title"
+
+    def test_expected_dashboards_present(self) -> None:
+        """The three expected dashboard files are present."""
+        names = {p.name for p in _DASHBOARDS_DIR.glob("*.json")}
+        assert "mt5cli-overview.json" in names
+        assert "mt5cli-trades.json" in names
+        assert "mt5cli-market.json" in names
+
+    def test_readme_exists(self) -> None:
+        """examples/grafana/README.md is present."""
+        assert (_EXAMPLES_DIR / "README.md").is_file()
+
+    def test_docker_compose_exists(self) -> None:
+        """examples/grafana/docker-compose.yml is present."""
+        assert (_EXAMPLES_DIR / "docker-compose.yml").is_file()
+
+    def test_datasource_provisioning_exists(self) -> None:
+        """Datasource provisioning YAML is present."""
+        assert (
+            _EXAMPLES_DIR / "provisioning" / "datasources" / "mt5cli-sqlite.yaml"
+        ).is_file()
+
+    def test_dashboard_provisioning_exists(self) -> None:
+        """Dashboard provisioning YAML is present."""
+        assert (_EXAMPLES_DIR / "provisioning" / "dashboards" / "mt5cli.yaml").is_file()