feat(zed): install the Zed editor with the Arch config

Seeds settings.json into the home directory with a tmpfiles 'C' rule, the
same route swaylock and waypaper take: Zed rewrites the file whenever a
setting is changed from its UI, so a store symlink would break saving.

nix-ld is what makes the language servers Zed downloads run here; the
alternative, zed-editor.fhsWithPackages, would cut them off from
project-level tooling out of a nix-shell.

modules/zed.nix

@@ -0,0 +1,157 @@
+# ABOUTME: Installs the Zed editor and seeds its user configuration.
+# ABOUTME: nix-ld is what makes the language servers Zed downloads run here.
+
+{ pkgs, ... }:
+
+let
+  # Zed rewrites this file whenever a setting is changed from its UI, so it is
+  # copied into the home directory rather than linked from the store.
+  zedSettings = pkgs.writeText "zed-settings.json" ''
+    {
+      "cli_default_open_behavior": "new_window",
+      "reduce_motion": "on",
+      "edit_predictions": {
+        "provider": "none"
+      },
+      "project_panel": {
+        "dock": "left"
+      },
+      "outline_panel": {
+        "dock": "left"
+      },
+      "git_panel": {
+        "dock": "left"
+      },
+      "base_keymap": "SublimeText",
+      "cursor_shape": "block",
+      "ui_font_size": 14,
+      "ui_font_family": "Hack Nerd Font",
+      "ui_font_features": {
+        "calt": true
+      },
+      "buffer_font_family": "Hack Nerd Font",
+      "buffer_font_size": 14,
+      "theme": {
+        "mode": "system",
+        "light": "Catppuccin Latte",
+        "dark": "Catppuccin Mocha"
+      },
+      "telemetry": {
+        "diagnostics": false,
+        "metrics": false
+      },
+      "terminal": {
+        "shell": {
+          "program": "zsh"
+        },
+        // LC_MESSAGES=C keeps tool output (git, pytest, ruff) in English so it
+        // stays greppable. Number and date formatting follows the system LANG.
+        "env": {
+          "LC_MESSAGES": "C"
+        }
+      },
+      "show_edit_predictions": false,
+      "toolbar": {
+        "quick_actions": false
+      },
+      "agent": {
+        "dock": "right",
+        "enabled": false,
+        "button": false
+      },
+      "chat_panel": {
+        "button": "never"
+      },
+      "collaboration_panel": {
+        "dock": "left",
+        "button": false
+      },
+      "auto_install_extensions": {
+        "catppuccin": true,
+        "dockerfile": true,
+        "html": true,
+        "log": true,
+        "nix": true,
+        "php": true,
+        "scss": true,
+        "vue": true
+      },
+      "languages": {
+        "Python": {
+          // ruff formats and organizes imports, basedpyright does type checking.
+          // The other three bundled servers are disabled explicitly: without the
+          // negations the "..." placeholder pulls in pyright, pylsp and ty as well,
+          // which means four type checkers reporting on the same file.
+          "language_servers": [
+            "ruff",
+            "basedpyright",
+            "!pyright",
+            "!pylsp",
+            "!ty",
+            "..."
+          ],
+          "formatter": {
+            "language_server": {
+              "name": "ruff"
+            }
+          },
+          "code_actions_on_format": {
+            "source.organizeImports.ruff": true
+          }
+        },
+        "JavaScript": {
+          "code_actions_on_format": {
+            "source.fixAll.eslint": true
+          }
+        },
+        "TypeScript": {
+          "code_actions_on_format": {
+            "source.fixAll.eslint": true
+          }
+        },
+        "TSX": {
+          "code_actions_on_format": {
+            "source.fixAll.eslint": true
+          }
+        },
+        "PHP": {
+          // Intelephense without a licence key: completion, diagnostics, hover,
+          // formatting and find-all-references are covered. Rename, code actions
+          // and inlay hints stay locked behind the paid tier.
+          "language_servers": [
+            "intelephense",
+            "!phpactor",
+            "!phptools",
+            "!phpantom",
+            "..."
+          ]
+        }
+      },
+      "lsp": {
+        "rust-analyzer": {
+          "initialization_options": {
+            "check": {
+              "command": "clippy"
+            }
+          }
+        }
+      }
+    }
+  '';
+in
+{
+  # CLI entry point is `zeditor`, not `zed`. Needs working Vulkan, the GUI does
+  # not start without it.
+  environment.systemPackages = [ pkgs.zed-editor ];
+
+  # Zed downloads its language servers into ~/.local/share/zed/languages/ and
+  # those binaries expect an FHS layout that does not exist here. nix-ld
+  # supplies the loader they look for — the route the NixOS wiki recommends,
+  # over zed-editor.fhsWithPackages, which would cut the servers off from
+  # project-level tooling coming out of a nix-shell.
+  programs.nix-ld.enable = true;
+
+  systemd.user.tmpfiles.rules = [
+    "C %h/.config/zed/settings.json 0644 - - - ${zedSettings}"
+  ];
+}