feat(viz): renderer shapes/iconos/flechas/edge-styles (issue 0049f)

graph_renderer 1.5.0:
- 6 shapes SDF (circle, square, diamond, hex, triangle, rounded square)
  con dispatch en fragment shader y AA via fwidth.
- Atlas opcional de iconos Tabler bakeado por graph_icons; el shader
  compone overlay desde un uniform vec4 u_icon_uvs[256]. Setter publico
  graph_renderer_set_icon_atlas(r, tex, uv_table, count).
- Aristas direccionales: 6 vertices por arista (line + chevron de la
  flecha) en una sola draw call; segmento principal acortado por el
  radio del nodo target.
- Edge styles solid/dashed/dotted via descarte por arc_length en el
  fragment shader; las lineas del chevron son siempre solidas.

graph_icons 1.0.0 (nuevo):
- Atlas RGBA8 512x512 = grid 16x16 (256 iconos max) bakeado con
  stb_truetype desde tabler-icons.ttf.
- API: graph_icons_build/texture/region/uv_table/destroy. icon_id es
  1-based; 0 reservado para "sin icono".
- Hook FN_GRAPH_ICONS_SKIP_GL=1 para tests sin contexto GL.

Demo demos_graph_styles en primitives_gallery: 6 EntityTypes (uno por
shape) con icono Tabler representativo + 3 RelationTypes (knows/uses/
owns) con flechas direccionales y los 3 estilos.

test_graph_icons: 6 casos cubriendo bake, regiones 1-indexed, uv_table
consistente, layout en grid 16x16, validacion de count fuera de rango,
y verificacion de alpha != 0 en las celdas tras bake.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cpp/apps/primitives_gallery/main.cpp

@@ -64,6 +64,7 @@ static const DemoEntry k_demos[] = {
     {"histogram",       "histogram",       "Viz",  &gallery::demo_histogram},
     {"sparkline",       "sparkline",       "Viz",  &gallery::demo_sparkline},
     {"graph_viewport",  "graph_viewport",  "Viz",  &gallery::demo_graph},
+    {"graph_styles",    "graph_styles",    "Viz",  &gallery::demo_graph_styles},   // issue 0049f
     {"candlestick",     "candlestick",     "Viz",  &gallery::demo_candlestick},
     {"gauge",           "gauge",           "Viz",  &gallery::demo_gauge},
     {"heatmap",         "heatmap",         "Viz",  &gallery::demo_heatmap},