docs(tier-1): add Tip Calculator beginner project

Projects/1-Beginner/Tip-Calculator-App.md

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+# Tip Calculator
+
+**Tier:** 1-Beginner
+
+Calculate a tip and total bill based on the bill amount, tip percentage, and number of people splitting the bill. This is a classic starter project to practice numeric input handling and basic UI updates.
+
+## User Stories
+
+-   [ ] User can enter the bill amount
+-   [ ] User can select a tip percentage (e.g., 5%, 10%, 15%, 20%, custom)
+-   [ ] User can enter number of people to split the bill
+-   [ ] User sees calculated tip amount and total per person update instantly
+-   [ ] User sees input validation errors for non-numeric or negative values
+
+## Bonus features
+
+-   [ ] Add preset percentage buttons and a custom percentage input
+-   [ ] Persist last used values in local storage
+-   [ ] Format currency based on locale
+-   [ ] Keyboard-only accessibility and screen reader friendly labels
+
+## Useful links and resources
+
+-   [Number() – MDN](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number)
+-   [Intl.NumberFormat – MDN](https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat)
+
+## Example projects
+
+-   [Build a Tip Calculator (YouTube)](https://www.youtube.com/results?search_query=tip+calculator+javascript)
+

README.md

@@ -78,6 +78,7 @@ required to complete them.
 | [Wind Chill](./Projects/1-Beginner/Windchill-App.md)                              | Calculate the windchill factor from an actual temperature  | 1-Beginner |
 | [Word Frequency](./Projects/1-Beginner/Word-Frequency-App.md)                     | Calculate word frequency in a block of text                | 1-Beginner |
 | [Weather App](./Projects/1-Beginner/Weather-App.md)                               | Get the temperature, weather condition of a city.          | 1-Beginner |
+| [Tip Calculator](./Projects/1-Beginner/Tip-Calculator-App.md)                     | Calculate tip/total per person for a bill                  | 1-Beginner |
 
 ### Tier-2: Intermediate Projects