feat(task-8): SECTION 25 grid and symbols - arch_grid, arch_symbol

engineering/arch/symbols.py is pure: grid_prims() draws each structural axis on
the grid role - its CENTER linetype comes from the A-GRID-E-N row, no primitive
sets one - with a 5 mm (paper) bubble and its label touching both ends, on the
symbol role so the circle does not print dashed. Numbers run along x and
letters along y (A..Z, AA, ... none skipped) unless labels names them;
positions are sorted, duplicates and label-count mismatches refused by path.

symbol_prims() draws the four plan symbols: the north arrow (a circle, an
arrow turned CCW from +Y, the vocab(lang) north letter upright beyond the tip),
the section mark (the cut line, a labelled bubble past each end and a viewing
arrow at each end, p1/p2 relative to the origin), the level mark (the triangle,
its line and the value formatted +3.00 / ±0.00, with a decimal comma in
Turkish) and the elevation mark (a circle whose pointers are the tangents from
r*sqrt(2) touching it at +/-45 degrees). An unknown kind is refused with the
list, a parameter the kind does not take with the ones it does. Every size is
a declared paper-mm drafting choice times the plot scale, not a standards value.

arch_grid and arch_symbol draw through draw_prims with ARCH_ROLE_LAYER; alias
records (COLUMNGRIDADD, English and Turkish synonyms), a regenerated inventory,
the README snapshot at 233 tools and the branch-local group snapshot
(entity_creation 21) complete the registration.

Beyond the plan: grid_axes refuses a labels value that is not a dict and a
labels.x / labels.y that is not a list (a string was split into one label per
character, a number raised a bare TypeError). No new ActiveX member: a live run
on AutoCAD 2026 (scratch document, closed after) drew the grid and all four
symbols through draw_prims - A-GRID-E-N created with CENTER, bubbles, texts and
symbols on A-SYMB-T-N, the Turkish north letter K and the level "+3,00".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

docs/tool-inventory.json

@@ -3,7 +3,7 @@
   "schema_version": 1,
   "package_version": "1.5.1",
   "totals": {
-    "tools": 231,
+    "tools": 233,
     "resources": 8,
     "prompts": 5,
     "groups": 25
@@ -16,7 +16,7 @@
     "dimensions": 5,
     "drawing": 11,
     "engineering": 10,
-    "entity_creation": 19,
+    "entity_creation": 21,
     "entity_modification": 16,
     "entity_query": 10,
     "environment": 22,
@@ -208,6 +208,34 @@
         "readOnlyHint": true
       }
     },
+    {
+      "name": "arch_grid",
+      "group": "entity_creation",
+      "cost": "mutate",
+      "summary": "Draw a structural grid: axis lines with numbered and lettered bubbles at both ends.",
+      "tags": [
+        "arch",
+        "create"
+      ],
+      "annotations": {
+        "title": "Architecture: Structural Grid",
+        "destructiveHint": false
+      }
+    },
+    {
+      "name": "arch_symbol",
+      "group": "entity_creation",
+      "cost": "mutate",
+      "summary": "Draw a plan symbol: north arrow, section mark, level mark or elevation mark.",
+      "tags": [
+        "arch",
+        "create"
+      ],
+      "annotations": {
+        "title": "Architecture: Symbol",
+        "destructiveHint": false
+      }
+    },
     {
       "name": "balloon_add",
       "group": "sheet",