feat(sheet): ISO 5457 frames and ISO 7200 title blocks for A4-A0

SECTION 24 opens with sheet_frame and titleblock_apply.

engineering/sheet/frames.py transcribes ISO 216's trimmed sizes, ISO 5457's
20 mm filing margin and 10 mm edges, the grid reference system (an even number
of divisions per side, that side of the frame over 50 mm; letters from the top,
numbers from the left), the centring marks (trimmed edge to 5 mm inside the
frame) and the 10 x 5 mm corner trimming marks. Every one of those numbers is
pinned by a test against the clause it comes from, because a wrong margin is
visible on every drawing this server makes.

engineering/sheet/titleblock.py draws the ISO 7200 block -- 180 mm wide, which
is exactly the drawing-space width of a portrait A4, which is why one block
fits every size -- and carries the ISO 128-30 projection-angle symbol. Which
symbol is which is derived rather than remembered: first-angle projection puts
the view seen from the left on the right, and the view of the cone from its
small end is the small circle inside the large one, so first angle draws the
cone left and the circles right.

The old A3 module folds in. apply_iso_a3_titleblock now forwards to
apply_titleblock(size="A3", projection=None, zones=False, marks=False), which is
the geometry it always drew, and tests/test_engineering_titleblock.py passes
unchanged -- that is the regression gate for the fold.

No new ActiveX member is called: both tools reach the drawing only through
contract members the A3 title block has used on both engines since v1.0
(entity_create_polyline / _line / _circle / _text, layout_list,
layout_set_current), so there was nothing to probe live.

Declared, not glossed: the zone divisions drawn here are equal, so ISO 5457's
allowance for shorter corner fields is not implemented; the division counts,
which are what a zone reference quotes, are the standard's. ISO 7200's full
optional-field list is not transcribed, only the fields this block has a cell
for. Coverage is A4-A0; an unknown size is refused by name with the five it has.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

tests/test_tool_registry.py

@@ -495,7 +495,7 @@ async def test_tool_groups_is_byte_identical_to_the_source_declared_grouping():
 
 
 async def test_tool_group_sizes_are_unchanged():
-    """Frozen snapshot of the surface (204 tools, 23 groups).
+    """Frozen snapshot of the surface (206 tools, 23 groups).
 
     Taken before @cad_tool landed at 131 tools; `batch` moved 2 -> 3 when
     v1.5.0's `cad_batch` joined `entity_batch_create`/`entity_batch_modify`, and
@@ -527,7 +527,14 @@ async def test_tool_group_sizes_are_unchanged():
     merge task tagged them, the four groups had filed those 28 tools under
     `layouts` / `templates` / `drawing` / `layers` / `view` / `system` by
     their secondary tags; those counts returned to their pre-track-E values
-    when the section tags landed.) Every other number here has been unchanged
+    when the section tags landed.)
+    `engineering` moved 10 -> 12 when v1.6's SECTION 24 opened with
+    `sheet_frame` and `titleblock_apply` (the ISO 5457 frame and the ISO 7200
+    title block for every size A4-A0). Both are tagged `engineering` and
+    `sheet`, and `sheet` is not in `_GROUP_TAG_PRIORITY`, so they file under
+    `engineering` beside `titleblock_apply_iso_a3` rather than opening a
+    24th group.
+    Every other number here has been unchanged
     since the snapshot was taken.
     """
     sizes = {label: len(names) for label, names in (await server._tool_groups()).items()}
@@ -538,7 +545,7 @@ async def test_tool_group_sizes_are_unchanged():
         "corner_ops": 4,
         "dimensions": 5,
         "drawing": 11,
-        "engineering": 10,
+        "engineering": 12,
         "entity_creation": 18,
         "entity_modification": 16,
         "entity_query": 9,
@@ -556,4 +563,4 @@ async def test_tool_group_sizes_are_unchanged():
         "validation": 1,
         "view": 4,
     }
-    assert sum(sizes.values()) == 204
+    assert sum(sizes.values()) == 206