feat(editor): Dear ImGui Embedded UI Implementation (RF6.1, RF6.2)

[LyeZinho]

Summary

• Implemented Dear ImGui integration for Caffeine Studio IDE
• Added ProfilerWindow with real-time frame time tracking and scope profiling
• Added ConsoleWindow with log filtering and auto-scroll
• Added StatsOverlay with FPS, frame metrics, and asset cache stats
• All editor modules are header-only and compile without SDL3/ImGui
• ImGui rendering guarded by CF_HAS_IMGUI, data structures always available

Changes

New Files

• src/editor/EditorTypes.hpp — FrameStats struct for frame metrics
• src/editor/ImGuiIntegration.hpp — ImGui integration with SDL3 + RHI
• src/editor/ProfilerWindow.hpp — Frame profiler with 120-frame history
• src/editor/ConsoleWindow.hpp — Log console with filtering
• src/editor/StatsOverlay.hpp — Real-time stats overlay
• tests/test_editor.cpp — 24 test cases for all editor components

Modified Files

• CMakeLists.txt — Added ImGui via FetchContent (v1.91.9)
• src/Caffeine.hpp — Included editor headers
• tests/CMakeLists.txt — Added test_editor.cpp
• docs/fase6/embedded-ui.md — Updated status to implemented

Implementation Details

ImGuiIntegration

• Initializes ImGui context with SDL3 and SDL_GPU backends
• Manages frame lifecycle (beginFrame/endFrame)
• Handles input capture detection (wantsKeyboard/wantsMouse)
• Processes SDL events and prevents input leakage to game

ProfilerWindow

• Tracks 120 frames of timing data with circular buffer
• Pause/resume functionality
• Integrates with Debug::Profiler for scope statistics
• Renders frame graph and scope table (when CF_HAS_IMGUI)

ConsoleWindow

• Stores log entries with level, category, and message
• Filter by log level (Trace/Info/Warn/Error/Fatal)
• Auto-scroll support
• Color-coded messages by severity

StatsOverlay

• Displays FPS, frame time, frame count
• Shows asset cache statistics (textures, audio, pending jobs)
• Transparent overlay window

Testing

• 24 test cases covering all data structures and API
• Tests verify data management without requiring ImGui
• All editor windows tested for open/close, pause/resume, filtering

Acceptance Criteria

• ✅ Dear ImGui integrado com SDL3 sem conflitos de input
• ✅ ProfilerWindow mostra dados do Profiler real-time
• ✅ ConsoleWindow filtra por nível e categoria
• ❌ Hot-reload: textura atualizada sem restart do jogo (future work)
• ✅ ImGui não interfere com input do jogo quando não em foco

Notes

• All code follows Caffeine style guidelines (header-only, closing namespace comments)
• Builds successfully with and without SDL3/ImGui
• No .cpp files created for editor module