feat(client): introduce Michroma font and implant UI theme (#517)

Add Michroma-Regular.ttf (OFL license) as the game font. Create
FontVariation with +1px tracking and a global Theme resource with
cyan-white (#E0F7FA) implant text color. Wire theme into project.godot
so all Label/RichTextLabel/Button/LineEdit nodes inherit automatically.
Add IMPLANT_TEXT_COLOR/DIM/PULSE constants to constants.gd.

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

client/project.godot

@@ -24,6 +24,11 @@ UIStrings="*res://scripts/autoloads/ui_strings.gd"
 FogState="*res://scripts/autoloads/fog_state.gd"
 AudioManager="*res://scripts/autoloads/audio_manager.gd"
 
+[gui]
+
+theme/custom="res://assets/theme/game_theme.tres"
+theme/custom_font="res://assets/fonts/michroma_ui.tres"
+
 [display]
 
 window/size/viewport_width=1920