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.osmodel

@@ -4,7 +4,7 @@
     "name": "OpenSees Ex 1a - 2D Elastic Cantilever Column",
     "description": "Original Ex 1a elastic cantilever column with shared gravity preload, static pushover, and BM68elc base-excitation cases.",
     "author": "OpenSees Wiki / Silvia Mazzoni & Frank McKenna",
-    "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": [
@@ -112,7 +113,8 @@
       ],
       "section_id": 1,
       "geom_transf": "Linear",
-      "rho": 0.0
+      "rho": 0.0,
+      "consistent_mass": false
     }
   ],
   "mp_constraints": [],
@@ -4138,7 +4140,8 @@
         0.0006658006,
         0.0006636009
       ],
-      "file_path": "BM68elc.acc"
+      "file_path": "BM68elc.acc",
+      "use_last": false
     }
   ],
   "load_patterns": [
@@ -4202,6 +4205,7 @@
       "pattern_ids": [
         1
       ],
+      "pattern_factors": {},
       "n_steps": 10,
       "load_factor_increment": 0.1,
       "system": "BandGeneral",
@@ -4219,6 +4223,7 @@
       "pattern_ids": [
         2
       ],
+      "pattern_factors": {},
       "control_node": 2,
       "control_dof": 1,
       "target_disp": 100.0,
@@ -4243,6 +4248,7 @@
       "pattern_ids": [
         3
       ],
+      "pattern_factors": {},
       "dt": 0.02,
       "n_steps": 1000,
       "system": "BandGeneral",
@@ -4258,6 +4264,8 @@
       "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