Prettier 2: Electric Boogaloo (#6113)

# Description of Changes
When I added Prettier formatting in #6052, my aim was to use just the
default settings in Prettier. Turns out, Prettier looks _really hard_
for any config files if it's not explicitly given one, which means that
if a developer has some sort of Prettier config file lying around on
their system, Prettier might find it and use it. Also, Prettier changes
its defaults based on stuff in `.editorconfig` without any good way of
disabling that behaviour explicitly in its config file.

To solve both of these issues, I've introduced a `.prettierrc` file
which sets Prettier's defaults explicitly, and then reformatted all our
code _again_ in Prettier's actual default settings. This should achieve
the aim of #6052 and remove the possibility for it breaking on different
dev computers.

frontend/eslint.config.mjs

@@ -10,7 +10,10 @@ const nodeGlobs = ["scripts/**/*.{js,ts,mjs}", "*.config.{js,ts,mjs}"];
 
 const baseRestrictedImportPatterns = [
   { regex: "^\\.", message: "Use @app/* imports instead of relative imports." },
-  { regex: "^src/", message: "Use @app/* imports instead of absolute src/ imports." },
+  {
+    regex: "^src/",
+    message: "Use @app/* imports instead of absolute src/ imports.",
+  },
 ];
 
 export default defineConfig(
@@ -64,7 +67,8 @@ export default defineConfig(
             ...baseRestrictedImportPatterns,
             {
               regex: "^@tauri-apps/",
-              message: "Tauri APIs are desktop-only. Review frontend/DeveloperGuide.md for structure advice.",
+              message:
+                "Tauri APIs are desktop-only. Review frontend/DeveloperGuide.md for structure advice.",
             },
           ],
         },