Add account sharing, Get Paid schedule, recurring manager, overspend warnings, mobile nav

Account sharing:
- fileStorage: add shares.json with createShare/listShares/getShareData/revokeShare
- /api/share/account: real implementation using session token
- /api/share/list: GET endpoint returning owned + received shares
- /api/share/data: GET endpoint to fetch a shared account's data
- SharedAccountManager: use session token, load existing shares, revoke support
- AccountManagement: render SharedAccountManager per-account
- page.tsx: load received shares on login, show "Shared with me" cards in Accounts view

Get Paid schedule:
- PaycheckSchedule type: weekly/biweekly/semimonthly/monthly with day config
- computeNextPayday(): calculates next payday from today
- Schedule UI in GetPaid modal with live "Next payday: ..." preview
- Schedule persisted to localStorage template

Recurring transaction manager:
- Fix biweekly support (was missing)
- Show "due now" vs "upcoming" with amber badge for overdue
- Render in Transactions view; onApplyRecurring creates new transactions + updates lastAppliedDate

Envelope overspending:
- Red warning banner at top of Envelopes view listing overspent envelopes
- Red ring on individual overspent envelope cards

Mobile layout:
- Fixed bottom tab bar (Home/Accounts/Txns/Envelopes/More) on sm: and below
- Active tab highlighted in blue
- Main content padded to avoid being hidden by bottom nav

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/fileStorage.ts

@@ -7,15 +7,27 @@ const DATA_DIR = path.join(process.cwd(), 'data');
 const USERS_FILE = path.join(DATA_DIR, 'users.json');
 const SESSIONS_FILE = path.join(DATA_DIR, 'sessions.json');
 const RESET_TOKENS_FILE = path.join(DATA_DIR, 'reset_tokens.json');
+const SHARES_FILE = path.join(DATA_DIR, 'shares.json');
 
 const ENCRYPTION_KEY = process.env.ENCRYPTION_KEY || 'default-key-change-in-production';
 const SESSION_TTL_MS = 30 * 24 * 60 * 60 * 1000; // 30 days
 const RESET_TOKEN_TTL_MS = 60 * 60 * 1000; // 1 hour
 
+interface Share {
+  ownerUserId: string;
+  ownerEmail: string;
+  targetEmail: string;
+  accountId: string;
+  role: 'view' | 'edit';
+  createdAt: string;
+}
+
+interface Shares { [shareId: string]: Share }
+
 async function initializeDirectories() {
   try {
     await fsPromises.mkdir(DATA_DIR, { recursive: true });
-    for (const file of [USERS_FILE, SESSIONS_FILE, RESET_TOKENS_FILE]) {
+    for (const file of [USERS_FILE, SESSIONS_FILE, RESET_TOKENS_FILE, SHARES_FILE]) {
       try {
         await fsPromises.access(file);
       } catch {
@@ -268,6 +280,67 @@ export class FileStorageService {
     }
   }
 
+  static async createShare(ownerUserId: string, ownerEmail: string, targetEmail: string, accountId: string, role: 'view' | 'edit'): Promise<string> {
+    const users = await readJson<Users>(USERS_FILE);
+    if (!Object.values(users).some(u => u.email === targetEmail)) {
+      throw new Error('No Capsule account found for that email address');
+    }
+    const releaseLock = await FileLock.acquire('shares-file');
+    try {
+      const shares = await readJson<Shares>(SHARES_FILE);
+      // Prevent duplicate shares for same account+email
+      const existing = Object.entries(shares).find(
+        ([, s]) => s.ownerUserId === ownerUserId && s.accountId === accountId && s.targetEmail === targetEmail
+      );
+      if (existing) return existing[0];
+      const shareId = crypto.randomUUID();
+      shares[shareId] = { ownerUserId, ownerEmail, targetEmail, accountId, role, createdAt: new Date().toISOString() };
+      await writeJson(SHARES_FILE, shares);
+      return shareId;
+    } finally {
+      releaseLock();
+    }
+  }
+
+  static async listShares(email: string, userId: string): Promise<{ received: Array<Share & { shareId: string }>; owned: Array<Share & { shareId: string }> }> {
+    const shares = await readJson<Shares>(SHARES_FILE);
+    const received = Object.entries(shares)
+      .filter(([, s]) => s.targetEmail === email)
+      .map(([shareId, s]) => ({ shareId, ...s }));
+    const owned = Object.entries(shares)
+      .filter(([, s]) => s.ownerUserId === userId)
+      .map(([shareId, s]) => ({ shareId, ...s }));
+    return { received, owned };
+  }
+
+  static async getShareData(shareId: string, requestorEmail: string): Promise<{ account: any; envelopes: any[]; transactions: any[] } | null> {
+    const shares = await readJson<Shares>(SHARES_FILE);
+    const share = shares[shareId];
+    if (!share || share.targetEmail !== requestorEmail) return null;
+    const data = await this.loadUserData(share.ownerUserId);
+    const account = data.accounts?.find((a: any) => a.id === share.accountId);
+    if (!account) return null;
+    const envelopes = (data.envelopes || []).filter((e: any) => e.accountId === share.accountId);
+    const transactions = (data.transactions || []).filter((t: any) => t.accountId === share.accountId);
+    return { account, envelopes, transactions };
+  }
+
+  static async revokeShare(shareId: string, requestorUserId: string): Promise<void> {
+    const releaseLock = await FileLock.acquire('shares-file');
+    try {
+      const shares = await readJson<Shares>(SHARES_FILE);
+      const share = shares[shareId];
+      if (!share) return;
+      if (share.ownerUserId !== requestorUserId && share.targetEmail !== requestorUserId) {
+        throw new Error('Not authorized to revoke this share');
+      }
+      delete shares[shareId];
+      await writeJson(SHARES_FILE, shares);
+    } finally {
+      releaseLock();
+    }
+  }
+
   private static async _createSession(userId: string, email: string): Promise<string> {
     const releaseLock = await FileLock.acquire('sessions-file');
     try {