chore: Update copilot instructions for npm usage and README template

Author: sejtam-dev

.github/copilot-instructions.md

@@ -432,20 +432,13 @@ Runs on every push and pull request to `main`:
 
 1. Checkout
 2. Node.js 20 setup with `npm` cache
-3. `npm install` (**not** `npm ci` — lock file generated on Windows is not compatible with the Linux runner)
+3. `npm ci`
 4. `npm run lint`
 5. `npm run build`
 
-> **Why `npm install` instead of `npm ci`?**
-> `npm ci` requires the lock file to be 100% in sync with the runner's platform. Since `package-lock.json`
-> is generated on Windows, platform-specific packages (e.g. `@swc/helpers`) may differ on the Linux CI
-> runner, causing `npm ci` to fail with `EUSAGE`. Using `npm install` resolves this transparently.
-
-### Vercel
-
-- Connected to GitHub — auto-deploys on push to `main`
-- No extra configuration needed for Next.js projects
-- Preview deployments are created for every PR automatically
+> **If `npm ci` fails with `EUSAGE` (lock file platform desync):**
+> Delete `node_modules/` and `package-lock.json` locally, run `npm install` to regenerate the lock file,
+> commit it and push. The CI runner will then be able to use `npm ci` successfully.
 
 ---
 
@@ -500,24 +493,80 @@ indent_style = tab
 }
 ```
 
-### README Badge Template
+### README.md template
 
 ```markdown
-[![CI](https://github.com/sejtam-dev/REPO/actions/workflows/ci.yml/badge.svg)](...)
+# [App Name]
+
+[![CI](https://github.com/sejtam-dev/REPO/actions/workflows/ci.yml/badge.svg)](https://github.com/sejtam-dev/REPO/actions/workflows/ci.yml)
 [![License: MIT](https://img.shields.io/badge/License-MIT-violet.svg)](./LICENSE)
-[![Live Demo](https://img.shields.io/badge/demo-URL-7c3aed)](https://URL)
+[![Live Demo](https://img.shields.io/badge/demo-live-7c3aed)](https://URL)
+
+> One-sentence description of what the project does and what it produces.
+
+## About
+
+2–3 sentences explaining the math / logic / concept behind the simulation or tool.
+What problem does it solve? What is the output?
+
+## Features
+
+- Feature one
+- Feature two
+- Feature three
+
+## Getting Started
+
+### Prerequisites
+
+- Node.js 20+
+- npm
+
+### Installation
+
+\`\`\`bash
+git clone https://github.com/sejtam-dev/REPO.git
+cd REPO
+npm install
+npm run dev
+\`\`\`
+
+Open [http://localhost:3000](http://localhost:3000) in your browser.
+
+### Build
+
+\`\`\`bash
+npm run build
+npm run start
+\`\`\`
+
+## Tech Stack
+
+| Layer      | Choice                  |
+|------------|-------------------------|
+| Framework  | Next.js 15 (App Router) |
+| Language   | TypeScript 5            |
+| Styling    | Tailwind CSS v4         |
+| Theme      | next-themes             |
+| i18n       | next-intl               |
+| Math       | KaTeX                   |
+| Charts     | Recharts                |
+
+## License
+
+MIT © [YEAR] [sejtam-dev](https://github.com/sejtam-dev)
 ```
 
 ### GitHub Description Template
 
 ```
-Interactive [what it does] — [one sentence about the output/goal]. Built with Next.js, TypeScript and Canvas API.
+Interactive [what it does] — [one sentence about the output/goal].
 ```
 
 ### GitHub Topics Template
 
 ```
-nextjs typescript tailwindcss canvas simulation math [domain-specific tags]
+nextjs typescript tailwindcss [domain-specific tags]
 ```
 
 ---
@@ -537,7 +586,6 @@ nextjs typescript tailwindcss canvas simulation math [domain-specific tags]
 | Add a key to only one `messages/*.json`                                | Add the key to **all** locale files simultaneously                                      |
 | Write math symbols as plain text (`π`, `y_c`, `θ`)                     | Use `$\\pi$`, `$y_c$`, `$\\theta$` in translations + `MathText` in JSX                  |
 | Use `\\\\pi` (four backslashes) in JSON                                | Use `\\pi` (two backslashes) — JSON needs one escape level, LaTeX needs one             |
-| Use `npm ci` in CI on a Windows-generated lock file                    | Use `npm install` — avoids platform-specific dependency mismatch                        |
 | Use inline script + custom ThemeContext for dark mode                  | Use `next-themes` — handles SSR, hydration and localStorage automatically               |
 | Read `document.documentElement.classList` during render                | Use `useTheme()` from `ThemeContext` which wraps `next-themes`                          |
 | Conditionally render different JSX for dark/light icon                 | Render both SVGs, control visibility with `dark:hidden` / `dark:block`                  |