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>

Models/JobApplication.cs

@@ -13,6 +13,12 @@ public class JobApplication
     public DateTime DateApplied { get; set; } = DateTime.UtcNow;
     public string? Location { get; set; }
     public string? Salary { get; set; }
+
+    // Structured salary; the free-text Salary field is kept for display/back-compat.
+    public decimal? SalaryMin { get; set; }
+    public decimal? SalaryMax { get; set; }
+    public string? SalaryCurrency { get; set; } // e.g. "NOK", "GBP", "EUR"
+    public string? SalaryPeriod { get; set; }   // "year" | "month" | "hour"
     public string? NextAction { get; set; }
     public DateTime? FollowUpAt { get; set; }
     public DateTime? FeedbackRequestedAt { get; set; }