Build a CRM to manage leads, deals and follow-ups

You are a senior full-stack developer who builds CRM systems. Build a CRM web app (mobile-friendly for salespeople on the move) with me, phase by phase.

## The business
- Business and what it sells: [DETAILS, e.g. real estate agency selling flats]
- Where leads come from: [website forms, Facebook lead ads, portals, walk-ins, calls]
- Sales team: [NUMBER] people with roles [e.g. owner, manager, sales executive]
- Pipeline stages: [e.g. new, contacted, site visit, negotiation, won, lost]
- Tech stack I prefer: [STACK or "you choose"]

## Features
1. Leads: capture by API and webhooks from each source, duplicate detection by phone and email, automatic assignment (round robin or by area or product), source tracking.
2. Contact and company records with full timeline: calls, notes, emails, WhatsApp messages, meetings, files, stage changes.
3. Pipeline as a drag-and-drop board and as a list with filters; deal value, expected close date, probability.
4. Tasks and follow-ups with reminders (in-app, email, push); a "today" screen for each salesperson; overdue follow-ups highlighted.
5. One-tap call and WhatsApp from the lead, with outcome logging.
6. Email templates and WhatsApp templates with merge fields; bulk messaging to segments.
7. Lost reasons, and automatic re-engagement reminders for lost or cold leads.
8. Reports: leads by source, conversion by stage and salesperson, response time, revenue forecast, activity per person.
9. Roles and permissions: salespeople see only their leads; managers see their team; owner sees everything.
10. Import and export by CSV, activity log, data backup.

## CRM rules
- First response time matters: alert the assigned person within a minute of a new lead.
- Every change to a lead is logged with who and when.
- Fast search across names, phones and emails even with 500,000 records.

## Quality rules (apply to every phase)
- Security: prepared statements or an ORM for every query, output escaping, CSRF tokens on every form, passwords hashed with bcrypt or Argon2, rate-limited login, role checks on the server for every admin route, file uploads checked by type and size and stored outside the web root or with random names, secrets only in an .env file.
- Validation: validate every input on the server (and also in the browser for speed). Show clear error messages next to the field that is wrong, and keep what the user already typed.
- Performance: pagination on every list, database indexes on every column used for search, filter or join, lazy-loaded and resized images (WebP), caching for pages that rarely change, no N+1 queries.
- Responsive and accessible: mobile first, works from 360px to wide desktop, proper labels on every form field, keyboard navigation, visible focus, colour contrast of at least 4.5:1, alt text on images.
- SEO: clean URLs, a unique title and meta description per page, canonical tags, Open Graph tags, schema.org JSON-LD where it applies, an XML sitemap and robots.txt.
- Code: small functions with clear names, one responsibility per file, comments only where the reason is not obvious, consistent formatting, no dead code.
- Errors: friendly error pages (404, 500), server errors written to a log, never shown to visitors.
- Deliver with: a README (install steps, .env example, how to create the first admin), database migrations and seed data with realistic sample content, and a deployment checklist.

## How to work with me
Do not write code yet. First reply with:
1. A short summary of what you understood, and anything in the brief that is unclear or contradictory (ask me, do not guess).
2. The final tech stack, with a one-line reason for each choice.
3. The folder and file structure.
4. The full database schema: every table, column, type, index and relation.
5. Every page or screen, and every API endpoint (method, path, who can call it, what it returns).
6. The build plan as numbered phases, each one small enough to finish and test on its own.

Wait for me to reply "go". Then build one phase at a time:
- For every file, give the full path and the complete code. Never write "...", "rest of the code stays the same" or TODO.
- After each phase, tell me how to run it, what to click to test it, and what is still missing. Then wait for me to reply "next".
- If you change a file you already gave me, give the whole updated file again.