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/ex1a_canti2d_eq.osmodel

@@ -4,7 +4,7 @@
     "name": "2D Elastic Cantilever EQ (OpenSees Ex 1a)",
     "description": "Elastic 2D cantilever with gravity preload + horizontal UniformExcitation time history from the A10000 record.",
     "author": "OpenSees Wiki / Examples Manual",
-    "units": "US (in, kip, kip·s²/in, s, ksi)"
+    "units": "Imperial (in, kip, kip·s²/in, s, ksi)"
   },
   "ndm": 2,
   "ndf": 3,
@@ -98,7 +98,8 @@
       "Iz": 1080000.0,
       "Iy": 1080000.0,
       "G": 1.0,
-      "J": 1.0
+      "J": 1.0,
+      "shape": null
     }
   ],
   "elements": [
@@ -112,9 +113,11 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     }
   ],
+  "mp_constraints": [],
   "time_series": [
     {
       "id": 1,
@@ -8121,7 +8124,8 @@
         -0.000147416,
         -0.000147326
       ],
-      "file_path": "A10000.txt"
+      "file_path": "A10000.txt",
+      "use_last": false
     }
   ],
   "load_patterns": [
@@ -8165,6 +8169,7 @@
       "pattern_ids": [
         1
       ],
+      "pattern_factors": {},
       "n_steps": 10,
       "load_factor_increment": 0.1,
       "system": "BandGeneral",
@@ -8182,6 +8187,7 @@
       "pattern_ids": [
         2
       ],
+      "pattern_factors": {},
       "dt": 0.01,
       "n_steps": 3995,
       "system": "BandGeneral",
@@ -8197,6 +8203,8 @@
       "max_iter": 10,
       "rayleigh_alpha_m": 0.0,
       "rayleigh_beta_k": 0.0,
+      "rayleigh_beta_k_init": 0.0,
+      "rayleigh_beta_k_comm": 0.0,
       "rayleigh_mode1_damping": 0.02,
       "preload_case_ids": [
         1