Fix ruff F402 and mark visual-map-field-strings gates as run

Rename the visual_map field loop variable so it does not shadow
dataclasses.field. ruff, pytest (641 passed, 1 skipped), and
docgen benchmark are green.

Co-authored-by: jmjava <jmjava@gmail.com>

Author: cursoragent

milestones/visual-map-field-strings.md

@@ -1,7 +1,7 @@
 # Milestone: visual_map type/scene/source and segment_names values must be strings
 
 **Status:** Active  
-**PR:** pending  
+**PR:** [#108](https://github.com/jmjava/documentation-generator/pull/108)  
 **Depends on:** `milestones/generation-model-strings.md` (PR #107),
 `milestones/visual-map-row-types.md` (PR #86),
 `milestones/segment-id-strings.md` (PR #87)
@@ -31,9 +31,9 @@ Fail closed at `Config.from_yaml`. Missing fields stay optional.
       be YAML strings (empty allowed).
 - [x] Present `segment_names` values must be non-empty YAML strings.
 - [x] Tests for list values of those keys.
-- [ ] `ruff check src/ tests/`
-- [ ] `pytest tests/`
-- [ ] `docgen benchmark` (no clock change)
+- [x] `ruff check src/ tests/`
+- [x] `pytest tests/`
+- [x] `docgen benchmark` (no clock change)
 
 ## Out of scope
 

src/docgen/config.py

@@ -250,11 +250,11 @@ def __post_init__(self) -> None:
                     f"{src}: visual_map.{sid_s} must be a YAML mapping, "
                     f"not {type(spec).__name__}"
                 )
-            for field in ("type", "scene", "class", "source"):
-                val = spec.get(field)
+            for fname in ("type", "scene", "class", "source"):
+                val = spec.get(fname)
                 if val is not None and not isinstance(val, str):
                     raise ConfigError(
-                        f"{src}: visual_map.{sid_s}.{field} must be a YAML string, "
+                        f"{src}: visual_map.{sid_s}.{fname} must be a YAML string, "
                         f"not {type(val).__name__}"
                     )
         wiz = self._block("wizard")