Implement story 2.2: coordinate projection and base map loading

Add MapBounds dataclass and equirectangular project() function in
projection.py, basemap.load() forcing pixels into memory via .copy(),
and full test coverage for both modules (4 new tests). All quality
gates pass: 67 tests, ruff clean.

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

tests/test_projection.py

@@ -1,2 +1,18 @@
-def test_placeholder() -> None:
-    pass
+from __future__ import annotations
+
+from planemapper.renderer.projection import MapBounds, project
+
+
+def test_home_projects_to_centre() -> None:
+    bounds = MapBounds(home_lat=53.0, home_lon=-6.0, radius_nm=100.0)
+    x, y = project(53.0, -6.0, bounds)
+    assert abs(x - 400) <= 2
+    assert abs(y - 240) <= 2
+
+
+def test_out_of_bounds_not_clamped() -> None:
+    bounds = MapBounds(home_lat=53.0, home_lon=-6.0, radius_nm=100.0)
+    # 10 degrees of lat north is far outside any 100nm bounds
+    x, y = project(63.0, -6.0, bounds)
+    # y should be well above display top (y < 0)
+    assert y < 0 or y > 480 or x < 0 or x > 800