refactor(edit): remove auto-indentation and add line-ending normalization

- [x] Remove auto-indentation from text mode edits (caller controls whitespace)
- [x] Add line-ending detection and normalization for both AST and text modes
- [x] Share edit logic via new `spliceContent` function for both modes
- [x] Fix diff to emit "No newline at end of file" markers
- [x] Fix diff to strip raw CR from CRLF file output
- [x] Remove double-unescape of backslash sequences in new_content
- [x] Fix countDiffLines to be hunk-aware (correctly count lines starting with +/-)
- [x] Fix block-comment stripping to remove standalone lines cleanly
- [x] Fix Python license header stripping to preserve separator blank lines

internal/server/server.go

@@ -313,7 +313,7 @@ func (s *Server) registerTools() {
 				mcp.Description("Edit operation: replace, insert_before, insert_after, delete"),
 			),
 			mcp.WithString("new_content",
-				mcp.Description("New content (required for replace/insert operations)"),
+				mcp.Description("New content (required for replace/insert operations). Inserted verbatim: send it as normal JSON (real newlines, quotes JSON-escaped as usual). The server does NOT re-interpret escape sequences, so backslash sequences in source code (e.g. \\n, \\t, \\\\ inside string literals, regexes, or Windows paths) are preserved exactly. Indentation is not auto-applied — include the leading whitespace you want. Line endings are normalized to the file's existing convention (LF or CRLF)."),
 			),
 			// AST-mode selectors (for code files)
 			mcp.WithString("selector_kind",