chore(flake): treefmt + deadnix/statix + pre-commit; relocate work module

- treefmt-nix drives `nix fmt` and the formatting check (nixfmt/shfmt/
  prettier; generated files and flake.lock excluded). Replaces the
  bespoke find-based check.
- deadnix and statix as flake checks and pre-commit hooks; deadnix
  ignores module-arg patterns, statix.toml disables the two house-style
  lints (repeated_keys, empty_pattern). Fixed the one real deadnix hit
  (unused overlay arg) and statix hit (use inherit for claude-code).
- git-hooks.nix installs the pre-commit gate via the devShell.
- .editorconfig for the base style.
- Move system/modules/work/default.nix -> lyrathorpe/home/work.nix (it is
  a home-manager module). README gains a Development section; docs
  reformatted by the new formatter.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.renovaterc.json

@@ -1,10 +1,6 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
-  "extends": [
-    "config:recommended",
-    ":dependencyDashboard",
-    ":semanticCommits"
-  ],
+  "extends": ["config:recommended", ":dependencyDashboard", ":semanticCommits"],
   "nix": {
     "enabled": true
   },