Follow the active theme in T3 Code

T3 Code reads themes an environment publishes into its state directory, so
a generated t3code.json carries the palette the same way claude.json and
vscode-theme.json already do, and omarchy-theme-set-t3code republishes it
on every theme change for the app to pick up live.

The template overrides only the roles a theme actually designs -- terminal
and code surfaces, text on canvas, borders, selection -- and leaves muted
text, placeholders, and status foregrounds to T3 Code, which contrast-solves
them against whatever canvas it is given. Overriding those directly cost
readability on light themes: White fell to 1.0:1 on placeholder text.

Installing from the menu now routes through omarchy-install-ai-t3-code so a
fresh install publishes the current palette and opens wearing it.

test/shell.d/theme-staging-test.sh

@@ -207,7 +207,7 @@ pass "a theme name cannot climb out of the theme directories"
 # generates. Every generated theme file is either denied to an installed theme or
 # recorded here as carrying colour, so a new template fails until it is placed.
 denied=(alacritty.toml foot.ini ghostty.conf kitty.conf gum_env.lua hyprland.lua neovim.lua vscode.json)
-colour_only=(btop.theme chromium.theme claude.json helix.toml hermes.yaml hyprland-preview-share-picker.css keyboard.rgb obsidian.css pi.json shell.toml vscode-theme.json)
+colour_only=(btop.theme chromium.theme claude.json helix.toml hermes.yaml hyprland-preview-share-picker.css keyboard.rgb obsidian.css pi.json shell.toml t3code.json vscode-theme.json)
 
 for tpl in "$ROOT"/default/themed/*.tpl; do
   generated=$(basename "$tpl" .tpl)