step 1: lock public api and pure core

README.md

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+# dpg-map
+
+`dpg-map` is a Dear PyGui map widget package under rebuild.
+
+The Step 1 public API contract is in place:
+
+```python
+import dpg_map as dpgm
+
+provider = dpgm.TileProvider(
+    name="custom",
+    url_template="https://example.com/{z}/{x}/{y}.png",
+    attribution="Tiles (c) Example",
+)
+dpgm.register_provider(provider)
+```
+
+Implemented in Step 1:
+
+- public package exports
+- tile provider definitions and registry
+- Web Mercator projection helpers
+- initial cache dataclasses
+- explicit stubs for GUI-dependent public functions
+
+GUI widget rendering and runtime state updates are planned for later rebuild steps.