feat: consolidate units to Metric/Imperial with unit-aware dialogs

- core/units: two dominant systems (Metric m/kN, Imperial ft/kip) with
  display conversion helpers, legacy 4-system migration in ProjectMeta
- dialogs/docks: unit-aware material, section, case, load, grid and
  results labels; diagram renderer unit labels; render controls update
- docs: add consistent_units.md; regen examples/*.osmodel artifacts
- tests: update persistence/phase8/project/unit-labels for new systems

examples/portal_pushover.osmodel

@@ -4,7 +4,7 @@
     "name": "Portal Pushover",
     "description": "",
     "author": "Ozan",
-    "units": "SI (m, N, kg, s, Pa)"
+    "units": "Metric (m, N, kg, s, Pa)"
   },
   "ndm": 3,
   "ndf": 6,
@@ -231,7 +231,8 @@
       "Iz": 0.000416,
       "Iy": 0.000129,
       "G": 80000000000.0,
-      "J": 2.04e-06
+      "J": 2.04e-06,
+      "shape": null
     }
   ],
   "elements": [
@@ -285,9 +286,11 @@
       ],
       "section_id": 3,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     }
   ],
+  "mp_constraints": [],
   "time_series": [
     {
       "id": 1,
@@ -327,6 +330,7 @@
       "pattern_ids": [
         1
       ],
+      "pattern_factors": {},
       "control_node": 3,
       "control_dof": 1,
       "target_disp": 0.15,
@@ -340,7 +344,8 @@
       "algorithm": "Newton",
       "test": "NormDispIncr",
       "tolerance": 1e-06,
-      "max_iter": 25
+      "max_iter": 25,
+      "preload_case_ids": []
     },
     {
       "id": 2,