feat: add data import from CSV and JSON

Import utility with CSV parser, Toggl/Clockify format mapping, and
generic CSV column mapping. Settings Data tab has import UI with
file picker, format selector, preview table, and import execution.

src/utils/import.ts

@@ -0,0 +1,83 @@
+export interface ImportEntry {
+  project_name: string
+  client_name?: string
+  task_name?: string
+  description?: string
+  start_time: string
+  end_time?: string
+  duration: number
+  tags?: string[]
+}
+
+export function parseCSV(text: string): string[][] {
+  const lines = text.split('\n').filter(l => l.trim())
+  return lines.map(line => {
+    const cells: string[] = []
+    let current = ''
+    let inQuotes = false
+    for (const char of line) {
+      if (char === '"') {
+        inQuotes = !inQuotes
+      } else if (char === ',' && !inQuotes) {
+        cells.push(current.trim())
+        current = ''
+      } else {
+        current += char
+      }
+    }
+    cells.push(current.trim())
+    return cells
+  })
+}
+
+export function parseDurationString(dur: string): number {
+  // Handle HH:MM:SS, HH:MM, or decimal hours
+  if (dur.includes(':')) {
+    const parts = dur.split(':').map(Number)
+    if (parts.length === 3) return parts[0] * 3600 + parts[1] * 60 + parts[2]
+    if (parts.length === 2) return parts[0] * 3600 + parts[1] * 60
+  }
+  const hours = parseFloat(dur)
+  if (!isNaN(hours)) return Math.round(hours * 3600)
+  return 0
+}
+
+export function mapTogglCSV(rows: string[][]): ImportEntry[] {
+  // Toggl CSV format: Description, Project, Client, Task, Tag, Start date, Start time, End date, End time, Duration
+  const header = rows[0].map(h => h.toLowerCase())
+  const descIdx = header.findIndex(h => h.includes('description'))
+  const projIdx = header.findIndex(h => h.includes('project'))
+  const clientIdx = header.findIndex(h => h.includes('client'))
+  const taskIdx = header.findIndex(h => h.includes('task'))
+  const tagIdx = header.findIndex(h => h.includes('tag'))
+  const startDateIdx = header.findIndex(h => h.includes('start date'))
+  const startTimeIdx = header.findIndex(h => h.includes('start time'))
+  const durationIdx = header.findIndex(h => h.includes('duration'))
+
+  return rows.slice(1).map(row => ({
+    project_name: row[projIdx] || 'Imported',
+    client_name: clientIdx >= 0 ? row[clientIdx] : undefined,
+    task_name: taskIdx >= 0 ? row[taskIdx] : undefined,
+    description: descIdx >= 0 ? row[descIdx] : undefined,
+    start_time: combineDateTime(row[startDateIdx], row[startTimeIdx]),
+    duration: durationIdx >= 0 ? parseDurationString(row[durationIdx]) : 0,
+    tags: tagIdx >= 0 && row[tagIdx] ? row[tagIdx].split(',').map(t => t.trim()) : undefined,
+  }))
+}
+
+export function mapGenericCSV(rows: string[][], mapping: Record<string, number>): ImportEntry[] {
+  return rows.slice(1).map(row => ({
+    project_name: row[mapping.project] || 'Imported',
+    client_name: mapping.client >= 0 ? row[mapping.client] : undefined,
+    task_name: mapping.task >= 0 ? row[mapping.task] : undefined,
+    description: mapping.description >= 0 ? row[mapping.description] : undefined,
+    start_time: row[mapping.start_time] || new Date().toISOString(),
+    duration: mapping.duration >= 0 ? parseDurationString(row[mapping.duration]) : 0,
+  }))
+}
+
+function combineDateTime(date: string, time: string): string {
+  if (!date) return new Date().toISOString()
+  if (!time) return new Date(date).toISOString()
+  return new Date(`${date} ${time}`).toISOString()
+}