chore: delete orphan config assets + log chromium/templates concerns

Two unreferenced asset files removed; two larger concerns deferred to
roadmap rows because they need more thought than a focused audit
allows.

Deleted:
- `features/apps/alacritty/config/alacritty.toml` — the alacritty
  module uses `programs.alacritty.settings` (Nix attrset) exclusively;
  nothing references the on-disk file. The neighbouring (already-empty)
  `themes/` directory goes with it.
- `themes/templates/mako.ini.tpl` — no script reads it.

Deferred to ROADMAP "Later":
- `features/apps/chromium/Default/Preferences` is deployed as a Home
  Manager symlink into chromium's mutable profile directory. Either
  silently replaced on first save or silently failing to write —
  either way the static defaults don't survive. The actual chromium
  theming work happens via managed policies in
  core/system/browser.nix. Needs chromium-internals knowledge to
  decide whether to remove or rework, so flagged rather than
  unilaterally deleted.
- `themes/templates/*.tpl` (the remaining 10 templates) are also
  apparently orphan — deployed via xdg.dataFile but unconsumed by any
  script. Likely vestigial from a pre-stylix templating system.
  Logged as a separate row to decide deletion vs documentation as
  user-reference assets.

Found during Pillar 8 audit of features/apps.

themes/templates/mako.ini.tpl

@@ -1,5 +0,0 @@
-include=~/.config/nomarchy/default/mako/core.ini
-
-text-color={{ foreground }}
-border-color={{ accent }}
-background-color={{ background }}