fix: escape newlines in WireManager.add_text

The KiCad s-expression parser rejects raw newline and carriage-return
characters inside quoted string literals — a multi-line text annotation
written through `add_text` produced a `.kicad_sch` file that eeschema
silently tolerated but `kicad-cli sch ...` refused with "Failed to load
schematic." The escape pass only handled backslashes and double quotes.

Add `\\n` → `\\\\n` and `\\r` → `\\\\r` to the same escape chain. Order
matters: backslashes are escaped first so we don't double-escape our
own escapes.

A new regression test (`test_escapes_newlines_in_multiline_text`)
checks both that the resulting quoted string literal contains no raw
newline characters and that the file round-trips cleanly through the
sexpdata parser.

End-to-end smoke: a 4-line annotation written through the patched
add_text now passes `kicad-cli sch erc` (exit 0) where the previous
behaviour failed parse.

Note: the same escape gap exists in `_make_hierarchical_label_text`
and `_make_sheet_pin_text` for unescaped quotes/newlines in the user-
supplied text. Not fixed here to keep this PR scoped to the documented
add_text bug; happy to fold it in if a reviewer prefers.

python/commands/wire_manager.py

@@ -1045,7 +1045,15 @@ class WireManager:
     ) -> bool:
         """Add a free-form text annotation (SCH_TEXT) to a KiCad schematic."""
         try:
-            text_escaped = text.replace("\\", "\\\\").replace('"', '\\"')
+            # KiCad's parser rejects raw newlines inside quoted string literals,
+            # so escape them along with backslashes and quotes. Order matters:
+            # backslashes first, otherwise we double-escape our own escapes.
+            text_escaped = (
+                text.replace("\\", "\\\\")
+                .replace('"', '\\"')
+                .replace("\n", "\\n")
+                .replace("\r", "\\r")
+            )
             uid = str(uuid.uuid4())
             font_attrs = f"\n\t\t\t\t(size {font_size} {font_size})"
             if bold: