feat: gate heavy solver JSON, field traceability API, GUI rod/export depth

- C: emit profiles/diagnostics/fourier only when enable flags are set; null otherwise
- API: fieldTraceability on case parse/default and solve; fix GET /solve/default options
- Tests: golden fingerprint, quality gates, C diagnostics invariants; cardQa mean empty guard
- Makefile: test-solver-sanitize ASan/UBSan target; README and COMPUTE_PLAN updates
- GUI: taper weight/MTS/guides/sinker round-trip, rod catalog, solver output toggles,
  results (profiles/diagnostics/Fourier/traceability), engineering checks and tabs
- Restore canonical WellName in base-case for regression; trace TaperGuidesCountArray

Made-with: Cursor

solver-c/tests/test_solver.c

@@ -173,6 +173,26 @@ static int test_zero_input_bounded(void) {
     return 0;
 }
 
+/* Gas fraction and chamber pressure invariants after valve/gas stepping */
+static int test_diagnostics_invariants(void) {
+    SolverInputs inputs;
+    fill_base_inputs(&inputs);
+    SolverOutputs outputs;
+    if (solver_run_fdm(&inputs, &outputs) != 0) {
+        return 1;
+    }
+    for (int i = 0; i < outputs.point_count; i++) {
+        const double g = outputs.gas_fraction[i];
+        if (g < -1e-6 || g > 1.0 + 1e-6) {
+            return 2;
+        }
+        if (!isfinite(outputs.chamber_pressure_pa[i])) {
+            return 3;
+        }
+    }
+    return 0;
+}
+
 /* FDM vs FEA peak polished load tolerance (regression gate) */
 static int test_fdm_fea_peak_tolerance(void) {
     SolverInputs inputs;
@@ -247,6 +267,12 @@ int main(void) {
         return 1;
     }
 
+    rc = test_diagnostics_invariants();
+    if (rc != 0) {
+        printf("test_diagnostics_invariants failed: %d\n", rc);
+        return 1;
+    }
+
     printf("solver-c tests passed\n");
     return 0;
 }