Rewrite documentation with new tagline (#805)

* docs: update tagline to "The reactive client-first store for your API"

Updated the tagline across documentation to reflect the new messaging from the 0.5 release blog post. The new tagline better emphasizes TanStack DB's client-first architecture and API-centric approach.

Files updated:
- README.md
- docs/overview.md
- docs/quick-start.md

* docs: expand tagline with value proposition and key benefits

Enhanced the new tagline with additional context about TanStack DB's
core value proposition: eliminating the need for custom API endpoints
while providing fast local queries, real-time reactivity, and optimistic
updates.

Key changes:
- Added "Stop building custom endpoints" messaging from 0.5 blog post
- Emphasized component-driven querying and flexibility
- Highlighted backend-agnostic nature (REST, sync engines, any source)
- Refined bullet points for clarity and consistency

Files updated:
- README.md - Added value prop and refined benefits list
- docs/overview.md - Expanded intro with value proposition
- docs/quick-start.md - Added tagline context for consistency

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: KyleAMathews

README.md

@@ -37,12 +37,14 @@
 
 > Tanstack DB is currently in BETA. See [the release post](https://tanstack.com/blog/tanstack-db-0.1-the-embedded-client-database-for-tanstack-query) for more details.
 
-A reactive client store that lets you build fast, sync‑driven apps with a backend‑agnostic real‑time data layer:
+The reactive client-first store for your API.
 
-- Blazing‑fast query engine for sub‑millisecond live queries, joins & aggregates
-- Fine‑grained reactivity to minimize component re‑rendering
-- Robust transaction primitives for optimistic mutations with sync & lifecycle support
-- Normalized data model that keeps backends simple and consistent
+Stop building custom endpoints for every view. TanStack DB lets you query your data however your components need it—with a blazing-fast local query engine, real-time reactivity, and instant optimistic updates:
+
+- Sub-millisecond live queries with joins & aggregates
+- Fine-grained reactivity to minimize re-rendering
+- Optimistic mutations with automatic rollback
+- Works with REST, sync engines, or any data source
 
 <a href="https://tanstack.com/db" style="font-weight:bold" >Read the docs →</a>
 <br />

docs/overview.md

@@ -7,7 +7,9 @@ id: overview
 
 Welcome to the TanStack DB documentation.
 
-TanStack DB is a reactive client store for building super fast apps on sync. It extends TanStack Query with collections, live queries and optimistic mutations.
+TanStack DB is the reactive client-first store for your API. Stop building custom endpoints for every view—TanStack DB lets you query your data however your components need it, with a blazing-fast local query engine, real-time reactivity, and instant optimistic updates.
+
+It extends TanStack Query with collections, live queries and optimistic mutations, working seamlessly with REST APIs, sync engines, or any data source.
 
 ## Contents
 

docs/quick-start.md

@@ -3,10 +3,10 @@ title: Quick Start
 id: quick-start
 ---
 
-TanStack DB is a reactive client store for building super fast apps. This example will show you how to:
+TanStack DB is the reactive client-first store for your API. Stop building custom endpoints for every view—query your data however your components need it. This example will show you how to:
 
 - **Load data** into collections using TanStack Query
-- **Query data** with blazing fast live queries
+- **Query data** with blazing-fast live queries
 - **Mutate data** with instant optimistic updates
 
 ```tsx