feat(shaders_lab): uniform annotations → auto-generated ImGui controls

- cpp/functions/gfx/uniform_parser: regex-based parser of @slider/@color/@toggle/@xy annotations (+ inline tests)
- cpp/functions/gfx/uniform_panel: ImGui widgets + value store + glUniform* apply
- shader_canvas: optional uniforms callback invoked per-frame
- gl_loader: +glUniform1i/3f/4f
- seed plasma: demo uniforms u_speed + u_color
- rebuild Windows .exe

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

cpp/apps/shaders_lab/main.cpp

@@ -3,11 +3,14 @@
 
 #include "gfx/shader_canvas.h"
 #include "gfx/gl_shader.h"
+#include "gfx/uniform_parser.h"
+#include "gfx/uniform_panel.h"
 #include "core/fps_overlay.h"
 #include "seed_shaders.h"
 
 #include <chrono>
 #include <string>
+#include <vector>
 
 static fn::gfx::ShaderCanvas g_canvas;
 static std::string g_source = PLASMA;
@@ -15,10 +18,14 @@ static std::string g_last_err;
 static int g_last_err_line = -1;
 static std::chrono::steady_clock::time_point g_last_edit;
 static bool g_dirty = true;
+static std::vector<fn::gfx::UniformDescriptor> g_descs;
+static fn::gfx::UniformStore g_store;
 
 static void try_compile() {
     auto r = fn::gfx::compile_fragment(g_source);
     if (r.ok) {
+        g_descs = fn::gfx::parse_uniforms(g_source);
+        fn::gfx::uniforms_sync(g_store, g_descs);
         fn::gfx::canvas_set_program(g_canvas, r.program);
         g_last_err.clear();
         g_last_err_line = -1;
@@ -91,13 +98,16 @@ static void render() {
 
     // --- Canvas panel ---
     if (ImGui::Begin("Canvas")) {
-        fn::gfx::canvas_render(g_canvas, static_cast<float>(ImGui::GetTime()));
+        fn::gfx::canvas_render(g_canvas, static_cast<float>(ImGui::GetTime()),
+            [](unsigned int program) {
+                fn::gfx::uniforms_apply(g_store, g_descs, program);
+            });
     }
     ImGui::End();
 
     // --- Controls panel ---
     if (ImGui::Begin("Controls")) {
-        ImGui::TextDisabled("Controls (fase 2)");
+        fn::gfx::uniforms_panel(g_store, g_descs);
         ImGui::Spacing();
         fps_overlay();
     }