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/cantilever.osmodel

@@ -4,7 +4,7 @@
     "name": "Cantilever",
     "description": "",
     "author": "Ozan",
-    "units": "SI (m, N, kg, s, Pa)"
+    "units": "Metric (m, N, kg, s, Pa)"
   },
   "ndm": 3,
   "ndf": 6,
@@ -198,7 +198,8 @@
       "Iz": 0.0002,
       "Iy": 4.5e-05,
       "G": 80000000000.0,
-      "J": 8.5e-07
+      "J": 8.5e-07,
+      "shape": null
     }
   ],
   "elements": [
@@ -212,7 +213,8 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     },
     {
       "id": 2,
@@ -224,7 +226,8 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     },
     {
       "id": 3,
@@ -236,7 +239,8 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     },
     {
       "id": 4,
@@ -248,7 +252,8 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     },
     {
       "id": 5,
@@ -260,9 +265,11 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     }
   ],
+  "mp_constraints": [],
   "time_series": [
     {
       "id": 1,
@@ -341,6 +348,7 @@
       "pattern_ids": [
         1
       ],
+      "pattern_factors": {},
       "n_steps": 1,
       "load_factor_increment": 1.0,
       "system": "BandGeneral",
@@ -358,6 +366,7 @@
       "pattern_ids": [
         2
       ],
+      "pattern_factors": {},
       "n_steps": 1,
       "load_factor_increment": 1.0,
       "system": "BandGeneral",