feat(render): style, GLSL line/text pipelines, staging batches, bitmap font

include/plot/render/style.hpp

@@ -0,0 +1,25 @@
+#pragma once
+#include <plot/core/color.hpp>
+
+namespace plot::render {
+
+/// Every colour and metric the renderer draws with. Defaults are the dark theme
+/// the plan's render smoke test asserts against; a caller swaps a field and the
+/// next frame picks it up, so nothing here is baked into a shader.
+struct Style {
+  Color background = Color::hex(0x101418);
+  Color grid_major = Color::hex(0x2A3038);
+  Color grid_minor = Color::hex(0x1C2126);
+  Color axis_line = Color::hex(0x8A94A6);
+  Color axis_text = Color::hex(0xC8D0DC);
+  Color cursor = Color::hex(0xFFB020);
+  Color measure_fill = Color::hex(0xFFB020, 0.15f);
+  f32 axis_font_px = 12.0f;
+  f32 grid_label_pad = 4.0f;
+  f32 line_width_px = 1.5f;
+  f32 dense_threshold_spp = 1.5f;  ///< spec §4.3: samples per pixel above which
+                                   ///< a trace is drawn from the LOD pyramid.
+  f32 tick_min_px = 60.0f;         ///< minimum spacing between major ticks.
+};
+
+}  // namespace plot::render