chore(linting): refresh configs and sweep auto-fix

Pull in the refreshed linter and tooling configs (editorconfig,
gitignore, gitattributes, prettierignore, prettierrc, markdownlint,
yamllint, env.example, dotnet-tools) and run prettier and markdownlint
in --fix / --write mode across the repo so the existing tree matches
the new rules.

- prettier 2-space indent on yaml/yml and json overrides, asterisk
  strong, underscore emphasis, proseWrap always
- markdownlint MD007 indent aligned to 2 and MD049 to underscore so
  prettier output stays passing
- preflight Block F also ignores CLAUDE.md (gitignored personal file)
- prettierignore extended to keep HellionChat.yaml manifest and the
  NuGet packages.lock.json out of the formatter

No semantic content changed; csharpier, build, full build-suite
(729/729) and the new prettier/markdownlint/yamllint checks all green.

.prettierrc.json

@@ -1,7 +1,35 @@
 {
     "printWidth": 120,
     "tabWidth": 4,
-    "proseWrap": "always",
+    "useTabs": false,
+    "semi": true,
     "singleQuote": false,
-    "endOfLine": "lf"
+    "trailingComma": "all",
+    "bracketSpacing": true,
+    "arrowParens": "always",
+    "proseWrap": "always",
+    "endOfLine": "lf",
+    "overrides": [
+        {
+            "files": "*.md",
+            "options": {
+                "printWidth": 100,
+                "tabWidth": 2
+            }
+        },
+        {
+            "files": ["*.yml", "*.yaml"],
+            "options": {
+                "tabWidth": 2,
+                "singleQuote": true
+            }
+        },
+        {
+            "files": "*.json",
+            "options": {
+                "tabWidth": 4,
+                "trailingComma": "none"
+            }
+        }
+    ]
 }