rules: file encoding for PowerShell (Windows) and shell (Linux)

Add alwaysApply file-encoding rule, shell-spec, .editorconfig and .gitattributes templates so agents save .ps1 as UTF-8 BOM+CRLF and .sh as UTF-8+LF; document runtime JSON/spool without BOM.

Co-authored-by: Cursor <cursoragent@cursor.com>

.editorconfig

@@ -0,0 +1,21 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+
+[*.ps1]
+charset = utf-8-bom
+end_of_line = crlf
+
+[*.psm1]
+charset = utf-8-bom
+end_of_line = crlf
+
+[*.sh]
+charset = utf-8
+end_of_line = lf
+
+[*.md]
+end_of_line = lf