Add constants for astronomical calculations and update benchmark links in documentation

- Introduced a new constants.php file containing various astronomical constants and flags used for calculations.
- Updated links in index.html to point correctly to the benchmark report, ensuring proper navigation for users.

Author: jayeshmepani

benchmark/UltimateBenchmark.php docs/benchmark/UltimateBenchmark.phpbenchmark/UltimateBenchmark.php renamed to docs/benchmark/UltimateBenchmark.php

@@ -1369,7 +1369,7 @@ <h2>Performance</h2>
           <div class="info-box" style="border-left-color: var(--primary); background: rgba(37, 99, 235, 0.05);">
             <h3>🚀 Interactive Performance Audit</h3>
             <p>We conducted a rigorous 106-function side-by-side benchmark comparing this FFI implementation against the native <code>kevindecapite/php-sweph</code> C-extension.</p>
-            <a href="../benchmark/benchmark.html" target="_blank" style="display: inline-block; margin-top: 1rem; padding: 0.75rem 1.5rem; background: var(--primary); color: white; border-radius: 0.5rem; text-decoration: none; font-weight: 700; transition: opacity 0.2s;">View Full FFI vs. C-Ext Report &rarr;</a>
+            <a href="benchmark/benchmark.html" target="_blank" style="display: inline-block; margin-top: 1rem; padding: 0.75rem 1.5rem; background: var(--primary); color: white; border-radius: 0.5rem; text-decoration: none; font-weight: 700; transition: opacity 0.2s;">View Full FFI vs. C-Ext Report &rarr;</a>
           </div>
           <div class="info-box">
             <h3>Tips for Optimal Performance</h3>
@@ -1442,7 +1442,7 @@ <h2>Comparison with Other Packages</h2>
           </table>
           <div style="margin-top: 2rem; text-align: center;">
             <p style="color: var(--text-muted); font-size: 0.9rem;">For bit-level accuracy and nanosecond-precision timing data:</p>
-            <a href="../benchmark/benchmark.html" target="_blank" style="color: var(--primary); font-weight: 600; text-decoration: underline;">Open the Deep Comparison Audit &rarr;</a>
+            <a href="benchmark/benchmark.html" target="_blank" style="color: var(--primary); font-weight: 600; text-decoration: underline;">Open the Deep Comparison Audit &rarr;</a>
           </div>
         </section>