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>

job-tracker-ui/src/salary.ts

@@ -0,0 +1,21 @@
+import { JobApplication } from "./types";
+
+type SalaryFields = Pick<JobApplication, "salary" | "salaryMin" | "salaryMax" | "salaryCurrency" | "salaryPeriod">;
+
+const PERIOD_SUFFIX: Record<string, string> = { year: "yr", month: "mo", hour: "hr" };
+
+/** Structured salary when present ("60 000–70 000 NOK/yr"), otherwise the free-text field. */
+export function formatSalary(job: SalaryFields): string | null {
+  const { salaryMin, salaryMax, salaryCurrency, salaryPeriod } = job;
+  if (salaryMin == null && salaryMax == null) {
+    return job.salary?.trim() || null;
+  }
+
+  const fmt = (value: number) => value.toLocaleString();
+  const range = salaryMin != null && salaryMax != null && salaryMin !== salaryMax
+    ? `${fmt(salaryMin)}–${fmt(salaryMax)}`
+    : fmt((salaryMin ?? salaryMax) as number);
+  const currency = salaryCurrency ? ` ${salaryCurrency}` : "";
+  const period = salaryPeriod ? `/${PERIOD_SUFFIX[salaryPeriod] ?? salaryPeriod}` : "";
+  return `${range}${currency}${period}`;
+}