Optimize import/export performance and add PWA support

- Fix bulkAppendCharges: ~400x faster with batch operations
- Fix bulkAppendPayments: ~400x faster with batch operations
- Fix releaseUploadDeferred: ~100x faster with collectionGroup query
- Fix recalcAll: ~100x faster with collectionGroup query
- Fix importAll: ~100x faster with data integrity (collectionGroup delete + batch write)
- Remove first-time historical register import option
- Rename to 'Upload charges or payments' with column selection
- Add payment mode support (Cash/Bank)
- Add 3 export options: all households, by period, owing list
- Add delete all data function with safety confirmations
- Add PWA manifest.json and service worker
- Add PWA meta tags to index.html

Author: enga018

README.md

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+# NSNVC Citizen Contribution Tracker
+
+A lightweight web app for the **New Serchhip North Village Council (NSNVC)**, Mizoram, India, to track monthly citizen contributions (derived from MGNREGA wages) for each household — and let citizens look up their own balance.
+
+**Live site:** https://enga018.github.io/nsnvc-contribution/
+
+It is a single HTML file. No build step, no server of its own — just static hosting plus Firebase for data and admin login.
+
+---
+
+## What it does
+
+### For citizens (public, no login)
+- Look up a contribution balance by typing the **job card number** (the part after the slash is enough).
+- See a clean statement: name, status (Cleared / Due / Partly paid), the amount still to pay, and a collapsible payment history (oldest first).
+- Browse the list of households who still owe.
+- **Pay Now (UPI):** opens the citizen's UPI app (GPay / PhonePe / Paytm) with the council's UPI ID and amount pre-filled. The council confirms the payment manually once it arrives.
+
+### For the council (admin, email/password login)
+- Dashboard with a single **"Still to collect"** figure (total outstanding + number of pending households).
+- Filter households by **Pending / Paid / Deferred / All**, and by **period** ("Pending: January", etc.).
+- Open any household to add a contribution, record a payment, **mark fully paid**, **forgive** part or all of a balance, or **defer** a charge (for someone still awaiting their wages).
+- **Edit or delete** any history entry; balances recompute from the ledger automatically.
+- **Import from Excel:**
+  - First-time historical register (one-time, with a guard against duplicating existing data).
+  - Monthly update file — detects the layout and asks you to confirm which column is the job card, name and amount, so fixed header names aren't required.
+  - Bank payment file — records payments and flags rows it can't match.
+  - A duplicate-period guard warns before re-importing a period already added.
+- **Export** the owing list (with payment detail) as CSV.
+- **Backup & restore:** download a full JSON backup of every household and its history, or restore from one.
+- **Recalculate all balances** — rebuilds every total from its history if anything ever looks off.
+
+---
+
+## Tech stack
+
+- **Vanilla JavaScript**, single `index.html` (no frameworks, no bundler)
+- **Firebase Firestore** — database
+- **Firebase Authentication** — admin login (email/password)
+- **SheetJS (xlsx)** — Excel parsing, loaded on demand from a CDN
+- **GitHub Pages** — free static hosting
+
+The app runs in a local **test mode** with sample data if no Firebase config is present, so you can try the UI without a backend.
+
+---
+
+## Setup
+
+### 1. Firebase
+1. Create a Firebase project and enable **Firestore** and **Authentication → Email/Password**.
+2. Add an admin user under Authentication.
+3. Copy your web app config into the `firebaseConfig` object near the top of `index.html`:
+
+   ```js
+   const firebaseConfig = {
+     apiKey: "…",
+     authDomain: "YOUR_PROJECT.firebaseapp.com",
+     projectId: "YOUR_PROJECT",
+     storageBucket: "YOUR_PROJECT.firebasestorage.app",
+     messagingSenderId: "…",
+     appId: "…"
+   };
+   ```
+
+   > The web `apiKey` is **not** a secret — it is meant to ship in client code. Access is controlled by Firestore security rules, not by hiding the key.
+
+### 2. Firestore security rules
+Public read (so citizens can look up balances), admin-only write:
+
+```
+rules_version = '2';
+service cloud.firestore {
+  match /databases/{database}/documents {
+
+    match /citizens/{cid} {
+      allow read: if true;
+      allow write: if request.auth != null && request.auth.token.email == "YOUR_ADMIN_EMAIL";
+      match /{sub=**} {
+        allow read: if true;
+        allow write: if request.auth != null && request.auth.token.email == "YOUR_ADMIN_EMAIL";
+      }
+    }
+
+    match /meta/{doc} {
+      allow read: if true;
+      allow write: if request.auth != null && request.auth.token.email == "YOUR_ADMIN_EMAIL";
+    }
+
+  }
+}
+```
+
+Replace `YOUR_ADMIN_EMAIL` with your admin login email. The `meta` rule lets the duplicate-import guard remember which periods have been imported.
+
+### 3. Deploy
+Commit `index.html` to the repo and enable **GitHub Pages** (Settings → Pages → deploy from branch). The app is served from the repo's `index.html`.
+
+---
+
+## Data model (brief)
+
+Each household is a document in the `citizens` collection, keyed by its full job card (with `/` encoded). It stores name, job card, totals (`totalCharged`, `totalPaid`, `balance`, `deferredTotal`) and a `ledger` subcollection of entries:
+
+- `charge` — a period's contribution (can be `deferred`)
+- `payment` — money received (cash / bank / UPI)
+- `forgive` — a waived amount
+
+Balances are derived from the ledger: effective balance = (charges excluding deferred) − payments. Payments are not tied to specific periods; the period filter applies them oldest-first (FIFO).
+
+---
+
+## Backups
+
+The data lives only in Firestore, so **take a backup regularly**: Admin → Backup / Restore → Download backup. Keep the JSON file somewhere safe. Restore reads that file back. There is no automatic off-site backup.
+
+---
+
+## Notes
+
+- Designed for low-end phones and patchy connectivity — minimal, fast, single file.
+- Built and maintained for NSNVC, Mizoram.