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/beam_quad_2d.osmodel

@@ -4,7 +4,7 @@
     "name": "Simply Supported Beam — Quad Elements (OpenSees Ex 6.4)",
     "description": "16×4 plane-stress quad mesh of a 40×10 deep beam with two midspan point loads, LoadControl 0→10 in 10 steps.",
     "author": "OpenSees Examples Manual",
-    "units": "US (in, kip, kip·s²/in, s, ksi)"
+    "units": "Imperial (in, kip, kip·s²/in, s, ksi)"
   },
   "ndm": 2,
   "ndf": 2,
@@ -3391,6 +3391,7 @@
       "b2": 0.0
     }
   ],
+  "mp_constraints": [],
   "time_series": [
     {
       "id": 1,
@@ -3441,6 +3442,7 @@
       "pattern_ids": [
         1
       ],
+      "pattern_factors": {},
       "n_steps": 10,
       "load_factor_increment": 1.0,
       "system": "ProfileSPD",
@@ -3456,6 +3458,7 @@
       "name": "FreeVibration",
       "type": "Transient",
       "pattern_ids": [],
+      "pattern_factors": {},
       "dt": 0.5,
       "n_steps": 1500,
       "system": "BandGeneral",
@@ -3471,6 +3474,8 @@
       "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