feat: structured salary fields (min/max/currency/period)

Adds SalaryMin/SalaryMax/SalaryCurrency/SalaryPeriod alongside the
existing free-text Salary field (kept for back-compat and display).

- JobApplication model + idempotent column bridging for SQLite and MySQL
- Create/Update DTOs with NormalizeSalary (clamps negatives, swaps
  inverted min/max, uppercases currency, whitelists period)
- JobApplicationDto exposes the fields; CSV export gains 4 columns
- UI: add/edit dialogs get min/max/currency/period inputs; job table
  renders a formatted range via shared salary.ts formatter (falls back
  to free-text when structured values are absent)
- EN/NB translations; backend + full frontend suites green

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

JobTrackerApi/Controllers/ExportController.cs

@@ -58,6 +58,10 @@ namespace JobTrackerApi.Controllers
                     "DateApplied",
                     "Location",
                     "Salary",
+                    "SalaryMin",
+                    "SalaryMax",
+                    "SalaryCurrency",
+                    "SalaryPeriod",
                     "NextAction",
                     "FollowUpAt",
                     "JobUrl",
@@ -76,6 +80,10 @@ namespace JobTrackerApi.Controllers
                         Esc(j.DateApplied.ToString("o")),
                         Esc(j.Location),
                         Esc(j.Salary),
+                        Esc(j.SalaryMin?.ToString(System.Globalization.CultureInfo.InvariantCulture)),
+                        Esc(j.SalaryMax?.ToString(System.Globalization.CultureInfo.InvariantCulture)),
+                        Esc(j.SalaryCurrency),
+                        Esc(j.SalaryPeriod),
                         Esc(j.NextAction),
                         Esc(j.FollowUpAt?.ToString("o")),
                         Esc(j.JobUrl),