feat: phase 3 - ledger and asset management

Add group expense tracking (ledger) and public asset inventory (asset) features.
Ledger supports income/expense recording with monthly summary. Asset tracks
group equipment with free-form holder transfer. Both are independent pages
accessible from GroupView navigation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/api/ledgers.ts

@@ -0,0 +1,132 @@
+// src/api/ledgers.ts
+import { pb } from './pocketbase'
+import type { Ledger } from '@/types'
+
+interface CreateLedgerData {
+  group: string
+  type: string
+  amount: number
+  category: string
+  description: string
+  relatedMembers?: string[]
+  occurredAt: string
+}
+
+interface ListLedgersOptions {
+  page?: number
+  limit?: number
+  type?: string
+  category?: string
+  month?: string
+}
+
+interface LedgerSummary {
+  totalIncome: number
+  totalExpense: number
+  balance: number
+}
+
+export async function createLedger(data: CreateLedgerData): Promise<Ledger> {
+  const user = pb.authStore.model
+  const record = await pb.collection('ledgers').create({
+    ...data,
+    creator: user?.id || '',
+    relatedMembers: data.relatedMembers || []
+  })
+  return record as unknown as Ledger
+}
+
+export async function listLedgers(
+  groupId: string,
+  options?: ListLedgersOptions
+): Promise<{ items: Ledger[]; total: number }> {
+  const { page = 1, limit = 30, type, category, month } = options || {}
+  let filter = `group="${groupId}"`
+  if (type) filter += ` && type="${type}"`
+  if (category) filter += ` && category="${category}"`
+  if (month) {
+    // month format: "2026-04"
+    const start = `${month}-01 00:00:00`
+    const year = parseInt(month.slice(0, 4))
+    const mon = parseInt(month.slice(5, 7))
+    // 下个月的第一天
+    const nextMonth = mon === 12 ? `${year + 1}-01` : `${year}-${String(mon + 1).padStart(2, '0')}`
+    const end = `${nextMonth}-01 00:00:00`
+    filter += ` && occurredAt>="${start}" && occurredAt<"${end}"`
+  }
+
+  const result = await pb.collection('ledgers').getList(page, limit, {
+    filter,
+    sort: '-occurredAt',
+    expand: 'creator,relatedMembers'
+  })
+  return { items: result.items as unknown as Ledger[], total: result.totalItems }
+}
+
+export async function updateLedger(
+  ledgerId: string,
+  data: Partial<CreateLedgerData>
+): Promise<Ledger> {
+  const record = await pb.collection('ledgers').update(ledgerId, data)
+  return record as unknown as Ledger
+}
+
+export async function deleteLedger(ledgerId: string): Promise<void> {
+  await pb.collection('ledgers').delete(ledgerId)
+}
+
+export async function getLedgerSummary(
+  groupId: string,
+  month?: string
+): Promise<LedgerSummary> {
+  let totalIncome = 0
+  let totalExpense = 0
+  let page = 1
+  const batchSize = 500
+  let hasMore = true
+
+  while (hasMore) {
+    let filter = `group="${groupId}"`
+    if (month) {
+      const start = `${month}-01 00:00:00`
+      const year = parseInt(month.slice(0, 4))
+      const mon = parseInt(month.slice(5, 7))
+      const nextMonth = mon === 12 ? `${year + 1}-01` : `${year}-${String(mon + 1).padStart(2, '0')}`
+      const end = `${nextMonth}-01 00:00:00`
+      filter += ` && occurredAt>="${start}" && occurredAt<"${end}"`
+    }
+
+    const result = await pb.collection('ledgers').getList(page, batchSize, {
+      filter,
+      fields: 'type,amount'
+    })
+
+    for (const item of result.items as any[]) {
+      if (item.type === 'income') {
+        totalIncome += item.amount || 0
+      } else if (item.type === 'expense') {
+        totalExpense += item.amount || 0
+      }
+    }
+
+    hasMore = result.items.length === batchSize && page * batchSize < result.totalItems
+    page++
+  }
+
+  return {
+    totalIncome,
+    totalExpense,
+    balance: totalIncome - totalExpense
+  }
+}
+
+export function subscribeLedgers(
+  groupId: string,
+  callback: (data: any) => void
+) {
+  return pb.collection('ledgers').subscribe('*', (data) => {
+    if (data.record?.group === groupId) {
+      callback(data)
+    }
+  })
+}