feat(template): ship Chromium by default; record product decisions

- home.packages: chromium active; mime → chromium-browser.desktop
- Decisions: markdown docs stay in-repo; PPD default confirmed
- Formatter + zram still open (explained in session, not closed)

V0: flake check --no-build green.

modules/home/mime.nix

@@ -50,13 +50,12 @@ lib.mkIf config.nomarchy.mime.enable {
       # The system-side Thunar (nomarchy.system.fileManager).
       "inode/directory" = "thunar.desktop";
 
-      # The template ships no browser by default (open Decision) — these
-      # are inert until one is installed; firefox is the template's first
-      # suggestion. A different browser registers its own handler and
-      # wins once these entries stay dead.
-      "text/html" = "firefox.desktop";
-      "x-scheme-handler/http" = "firefox.desktop";
-      "x-scheme-handler/https" = "firefox.desktop";
+      # Template ships chromium (chromium-browser.desktop). Entry is
+      # skipped by GIO if the package is deleted; install another browser
+      # and/or override these keys to retarget.
+      "text/html" = "chromium-browser.desktop";
+      "x-scheme-handler/http" = "chromium-browser.desktop";
+      "x-scheme-handler/https" = "chromium-browser.desktop";
     };
   };
 }