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.

scripts/preflight.sh

@@ -27,6 +27,6 @@ dotnet csharpier check HellionChat/
 echo "==> preflight: Block F — markdownlint"
 # npx --yes avoids a global install; first run caches into ~/.npm/_npx/.
 # Subsequent runs are sub-second.
-npx --yes markdownlint-cli2 "**/*.md" "#node_modules" "#bin" "#obj" "#.claude"
+npx --yes markdownlint-cli2 "**/*.md" "#node_modules" "#bin" "#obj" "#.claude" "#CLAUDE.md"
 
 echo "==> preflight: ALL GREEN"