Add proportional fonts, edit modes, and TOML config

- Add three proportional serif fonts: Crimson Pro, ET Book, Spectral
- Fix text rendering for variable-width fonts: selection, cursor,
  mouse click mapping, search highlights, and syntax-colored text
  now use pixel-accurate measurement via ImGui::CalcTextSize()
- Add per-buffer edit mode (code/writing) with auto-detection from
  file extension (.txt, .md, .rst, .org, .tex default to writing)
- Add C-k m keybinding and :mode command to toggle edit modes
- Switch config format from INI to TOML (kge.toml), with legacy
  INI fallback; vendor toml++ v3.4.0
- New config keys: font.code and font.writing for per-mode defaults
- Add font tab completion for ImGui builds
- Add tab completion for :mode command
- Update help text, themes.md, and add CONFIG.md
- Bump version to 1.10.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fonts/FontList.h

@@ -3,6 +3,8 @@
 #include "BerkeleyMono.h"
 #include "BrassMono.h"
 #include "BrassMonoCode.h"
+#include "CrimsonPro.h"
+#include "ETBook.h"
 #include "FiraCode.h"
 #include "Go.h"
 #include "IBMPlexMono.h"
@@ -13,6 +15,7 @@
 #include "IosevkaExtended.h"
 #include "ShareTech.h"
 #include "SpaceMono.h"
+#include "Spectral.h"
 #include "Syne.h"
 #include "Triplicate.h"
 #include "Unispace.h"

fonts/FontRegistry.cc

@@ -45,6 +45,16 @@ InstallDefaultFonts()
 		BrassMonoCode::DefaultFontBoldCompressedData,
 		BrassMonoCode::DefaultFontBoldCompressedSize
 	));
+	FontRegistry::Instance().Register(std::make_unique<Font>(
+		"crimsonpro",
+		CrimsonPro::DefaultFontRegularCompressedData,
+		CrimsonPro::DefaultFontRegularCompressedSize
+	));
+	FontRegistry::Instance().Register(std::make_unique<Font>(
+		"etbook",
+		ETBook::DefaultFontRegularCompressedData,
+		ETBook::DefaultFontRegularCompressedSize
+	));
 	FontRegistry::Instance().Register(std::make_unique<Font>(
 		"fira",
 		FiraCode::DefaultFontRegularCompressedData,
@@ -95,6 +105,11 @@ InstallDefaultFonts()
 		SpaceMono::DefaultFontRegularCompressedData,
 		SpaceMono::DefaultFontRegularCompressedSize
 	));
+	FontRegistry::Instance().Register(std::make_unique<Font>(
+		"spectral",
+		Spectral::DefaultFontRegularCompressedData,
+		Spectral::DefaultFontRegularCompressedSize
+	));
 	FontRegistry::Instance().Register(std::make_unique<Font>(
 		"syne",
 		Syne::DefaultFontRegularCompressedData,

fonts/FontRegistry.h

@@ -1,10 +1,12 @@
 #pragma once
 
+#include <algorithm>
 #include <cassert>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <unordered_map>
+#include <vector>
 
 #include "Font.h"
 
@@ -87,6 +89,19 @@ public:
 	}
 
 
+	// Return all registered font names (sorted)
+	std::vector<std::string> FontNames() const
+	{
+		std::lock_guard lock(mutex_);
+		std::vector<std::string> names;
+		names.reserve(fonts_.size());
+		for (const auto &[name, _] : fonts_)
+			names.push_back(name);
+		std::sort(names.begin(), names.end());
+		return names;
+	}
+
+
 	// Current font name/size as last successfully loaded via LoadFont()
 	std::string CurrentFontName() const
 	{