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.

.gitattributes

@@ -0,0 +1,51 @@
+# Normalize all text files to LF on commit and checkout.
+# Prevents CRLF drift when contributors work on Windows with core.autocrlf=true.
+* text=auto eol=lf
+
+# Python and shell — LF everywhere, shebangs require it on Unix.
+*.py   text eol=lf
+*.sh   text eol=lf
+
+# Web / config — LF.
+*.ts    text eol=lf
+*.tsx   text eol=lf
+*.js    text eol=lf
+*.jsx   text eol=lf
+*.mjs   text eol=lf
+*.cjs   text eol=lf
+*.json  text eol=lf
+*.yml   text eol=lf
+*.yaml  text eol=lf
+*.toml  text eol=lf
+*.md    text eol=lf
+*.html  text eol=lf
+*.css   text eol=lf
+
+# KiCad project files are text (S-expressions / JSON) — LF.
+*.kicad_sch  text eol=lf
+*.kicad_pcb  text eol=lf
+*.kicad_pro  text eol=lf
+*.kicad_sym  text eol=lf
+*.kicad_mod  text eol=lf
+*.kicad_dru  text eol=lf
+*.kicad_wks  text eol=lf
+*.net        text eol=lf
+
+# Windows-native scripts — must stay CRLF.
+*.bat text eol=crlf
+*.cmd text eol=crlf
+*.ps1 text eol=crlf
+
+# Binary assets — never touch.
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.pdf binary
+*.zip binary
+*.gz  binary
+*.woff  binary
+*.woff2 binary
+*.ttf   binary
+*.otf   binary