feat(fcitx5): switch CN/EN with Ctrl+Space and right Shift

Clear AltTriggerKeys, whose Shift_L default toggled on left Shift. Left Shift is now a plain modifier and right Shift switches through the shared Rime config.

home/linux/gui/base/fcitx5/README.md

@@ -2,11 +2,24 @@
 
 fcitx5 is enabled in `default.nix` with the [flypy](https://flypy.com/) Rime schema (Chinese),
 `fcitx5-mozc-ut` (Japanese), and `fcitx5-hangul` (Korean), alongside the US keyboard layouts. The
-Rime data ships in the [`overlays/fcitx5`](../../../../../overlays/fcitx5/) overlay.
+Rime data comes from the `rime-data-flypy` package in `nur-ryan4yin` (`pkgs/rime-data-flypy`); the
+whole Rime configuration, including the `fcitx5-rime` addon and the user customisation shared with
+macOS, lives in `home/base/gui/rime/` (see its README).
 
 ## Available Configurations
 
+- `fcitx5/config` (global config) → `~/.config/fcitx5/config`; pins `AltTriggerKeys` (see below).
 - `profile` → Symlink will be created at: `~/.config/fcitx5/profile`
 - `mozc-config1.db` (Mozc config) → Symlink will be created at: `~/.config/mozc/config1.db`
   - Main changes from the defaults: use half-width for all alphabets, numbers, and punctuation.
   - https://github.com/google/mozc/blob/2.30.5544.102/docs/configurations.md
+
+## Shift keys
+
+- Right Shift: switch CN/EN, through Rime.
+- Left Shift: plain modifier.
+- Ctrl+Space: switch CN/EN (fcitx5's `TriggerKeys`).
+
+fcitx5's `AltTriggerKeys` (the "temporarily toggle input method" hotkey) defaults to `Shift_L`, so
+it would toggle on left Shift; it is empty here. The Rime side, `Shift_R` as `commit_code` and
+`Shift_L` as `noop`, is in `home/base/gui/rime/flypy.custom.yaml` (shared with macOS).

home/linux/gui/base/fcitx5/default.nix

@@ -1,4 +1,8 @@
-{ config, pkgs, ... }:
+{
+  config,
+  pkgs,
+  ...
+}:
 {
   catppuccin.fcitx5.enable = false;
   xdg.configFile = {
@@ -8,16 +12,20 @@
       # so we need to force replace it in every rebuild to avoid file conflict.
       force = true;
     };
+    # `AltTriggerKeys` (the "temporarily toggle input method" hotkey) would
+    # toggle on left Shift, its default being Shift_L. Keep it empty so only
+    # right Shift (through Rime) and Ctrl+Space switch CN/EN. force = true
+    # because fcitx5 rewrites this file at runtime, like `profile`.
+    "fcitx5/config" = {
+      text = ''
+        [Hotkey/AltTriggerKeys]
+      '';
+      force = true;
+    };
     "mozc/config1.db".source =
       config.lib.file.mkOutOfStoreSymlink "${config.home.homeDirectory}/nix-config/home/linux/gui/base/fcitx5/mozc-config1.db";
   };
 
-  xdg.dataFile."fcitx5/rime/default.custom.yaml".text = ''
-    patch:
-      ascii_composer/switch_key/Shift_L: noop
-      ascii_composer/switch_key/Shift_R: commit_code
-  '';
-
   i18n.inputMethod = {
     enable = true;
     type = "fcitx5";
@@ -26,9 +34,9 @@
       qt6Packages.fcitx5-configtool # GUI for fcitx5
       fcitx5-gtk # gtk im module
 
-      # Chinese
-      fcitx5-rime # for flypy chinese input method
-      # fcitx5-chinese-addons # we use rime instead
+      # Chinese: the flypy (小鹤音形) fcitx5-rime addon is wired in
+      # home/base/gui/rime/default.nix, which is also where the rime-data-flypy
+      # package is resolved. fcitx5-chinese-addons is not used.
 
       # Japanese
       # ctrl-i / F7 - convert to takakana