chore: enforce LF line endings via gitattributes, editorconfig, pre-commit

Introduces a three-layer defence against CRLF/LF drift:

- `.gitattributes` normalizes all text files to LF on commit and checkout;
  Windows-native scripts (*.bat, *.cmd, *.ps1) explicitly keep CRLF.
- `.editorconfig` instructs editors (VS Code, JetBrains, vim, etc.) to save
  with LF by default so the problem is prevented at the source.
- `mixed-line-ending --fix=lf` hook in pre-commit catches anything that
  slips through and auto-fixes it before commit.

No file contents are normalized in this commit — that follows in a
separate `git add --renormalize .` commit for easier review.

.editorconfig

@@ -0,0 +1,21 @@
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[*.{ts,tsx,js,jsx,mjs,cjs,json,yml,yaml,md,html,css}]
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false
+
+[*.{bat,cmd,ps1}]
+end_of_line = crlf
+
+[Makefile]
+indent_style = tab