Move Executive Summary from Concepts to Introduction section

The Executive Summary provides a book-level overview for data architects
and technical leaders, which fits better in the Introduction rather than
being specific to the Concepts section.

Changes:
- Moved file from 20-concepts/00-0-executive-summary.md to
  00-introduction/05-executive-summary.md
- Updated section references to properly point to Concepts from Introduction
- Positioned after Purpose (00) to give architects quick access to
  high-level technical overview

Author: claude

…ok/20-concepts/00-0-executive-summary.md …/00-introduction/05-executive-summary.mdbook/20-concepts/00-0-executive-summary.md renamed to book/00-introduction/05-executive-summary.md book/20-concepts/00-0-executive-summary.md renamed to book/00-introduction/05-executive-summary.md

@@ -61,7 +61,7 @@ The core is fully open source. Organizations can build DIY solutions or use mana
 
 This book provides comprehensive coverage of DataJoint from foundations through advanced applications:
 
-**Part I: Concepts** (this section)
+**Part I: Concepts**
 - Database fundamentals and why they matter for scientific work
 - Data models: schema-on-write vs. schema-on-read, and why schemas enable mathematical guarantees
 - Relational theory: the 150-year mathematical foundation from De Morgan through Codd
@@ -112,7 +112,7 @@ DataJoint has been proven at scale: the MICrONS project used it to coordinate pe
 
 ## Getting Started
 
-The remaining chapters in this Concepts section build the theoretical foundation. If you prefer to learn by doing, the hands-on tutorial in **Relational Practice** provides immediate experience with a working database. The **Design** section then covers practical schema construction.
+The **Concepts** section builds the theoretical foundation. If you prefer to learn by doing, the hands-on tutorial in **Relational Practice** provides immediate experience with a working database. The **Design** section then covers practical schema construction.
 
 The [Blob Detection example](../80-examples/075-blob-detection.ipynb) demonstrates a complete image processing pipeline with all table tiers (Manual, Lookup, Imported, Computed) working together, providing a concrete reference implementation.