docs(paradigms): add detailed explanation of Declarative Programming with Java examples

What
- Documented the concept of **Declarative Programming** vs **Imperative Programming**.
- Highlighted key characteristics:
  - Focus on *what* to achieve, not *how* to achieve it.
  - High-level abstraction with less boilerplate code.
  - Execution strategy left to underlying system (e.g., SQL engine, Streams).
- Provided concrete examples across multiple domains:
  - **SQL** → `SELECT * FROM students WHERE marks > 90` (declarative query).
  - **Java Streams** → `list.stream().filter(...).map(...).toList()` (functional transformations).
  - **HTML/CSS** → structure and styling declaratively described.
- Outlined benefits:
  - Conciseness, readability, maintainability.
  - Easier parallelization via declarative APIs.
- Added **Java-specific comparison**:
  - Imperative sum of even numbers (loops + conditions).
  - Declarative sum using Streams API (`filter`, `mapToInt`, `sum`).

Why
- Declarative programming is central to modern Java (Streams, Lambdas, functional style).
- Developers often confuse *control flow* with *business logic*; declarative style separates the two.
- This doc clarifies when and why declarative approaches are preferred in enterprise apps.

Logic
1. **Definition**
   - Declarative = specify outcome, not steps.
   - Contrasted with imperative = specify exact flow (loops, state changes).

2. **Key Characteristics**
   - Abstraction of execution.
   - Focus on results instead of algorithmic details.
   - Reduction of verbosity and control structures.

3. **Examples**
   - SQL → declare query logic without procedural fetch.
   - Streams → pipelines describe transformation, not iteration.
   - HTML → structure declaration, not rendering process.

4. **Java Focus**
   - Streams API embodies declarative patterns (map/filter/reduce).
   - Shows improved readability and parallelization compared to traditional loops.

Real-life applications
- **Database queries (SQL)**: write intent-driven queries, let DBMS handle execution plan.
- **Back-end APIs (Java Streams)**: declarative transformations for business rules.
- **UI layer (HTML/CSS)**: declaratively specify layout and style, browsers handle rendering.
- **Parallel data processing**: declarative pipelines allow frameworks to optimize multithreaded execution.

Notes
- Declarative ≠ “no control,” but rather offloading control to libraries/engines.
- Imperative code is sometimes necessary for low-level optimization, but declarative style is preferred for clarity.
- Java’s `Stream.parallel()` demonstrates how declarative style enables automatic performance improvements.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan