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.

.markdownlint.json

@@ -1,9 +1,17 @@
 {
-    "MD007": { "indent": 4 },
+    "MD003": { "style": "atx" },
+    "MD004": { "style": "dash" },
+    "MD007": { "indent": 2 },
+    "MD009": { "br_spaces": 2, "strict": false, "list_item_empty_lines": false },
     "MD013": false,
     "MD024": { "siblings_only": true },
     "MD029": false,
     "MD033": false,
     "MD036": false,
-    "MD041": false
+    "MD040": true,
+    "MD041": false,
+    "MD046": { "style": "fenced" },
+    "MD048": { "style": "backtick" },
+    "MD049": { "style": "underscore" },
+    "MD050": { "style": "asterisk" }
 }