feat(python): text and dimension styles (doc.text_styles, doc.dim_styles)

Extends TableOperation with text style create/modify, dimension style
create/modify (DimStyle fields as a validated JSON object), rename, delete and
set-current. Reuses OCS's style in-use scan and reference-following rename
(four style_ops methods widened to pub(super)); a renamed text style also
updates dimension styles that name it. Real-IPC audit with DWG/DXF persistence
and undo, IPC and Python unit tests, docs. Four cadcodec findings are pinned by
canaries.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/cadcodec-reader-gaps.md

@@ -195,3 +195,17 @@ These are format constraints or OCS-side issues, not reader bugs:
 - **Spline weights in DXF** were briefly suspected but are correct: the writer
   emits group 41 only when `flags.rational` is set, so the host must set that
   flag when weights are present (fixed in OCS).
+
+### Text and dimension style findings (2026-09-21, not filed)
+
+Found by `audit_python_text_and_dim_styles_over_real_ipc`; each is pinned by a canary.
+
+- **`STYLE` generation flags:** the DXF writer hard-codes group 71 to 0, so a text
+  style's `flags.backward` and `flags.upside_down` are lost on every DXF save (DWG keeps them).
+- **`STYLE` oblique angle units:** group 50 is written and read as the raw radian value, while DXF
+  defines it in degrees; it round-trips inside cadcodec but AutoCAD would read 15 degrees as 0.26.
+  DWG stores radians correctly.
+- **`DIMSTYLE` text style name:** the DXF reader keeps only the text-style handle (group 340) and never
+  resolves `dimtxsty` from it, so the name reopens as `Standard` (the handle is right; DWG resolves both).
+- **`TextStyle::true_type_font`** is never written or read by either codec, so it lives only in memory.
+