refactor: update terminology in iApp building guides

- Changed section titles and descriptions to remove "Low-Level" terminology, simplifying the language for better clarity.
- Updated links in the main guide to reflect the new overview page for advanced iApp building.

Author: Le-Caignec

src/guides/build-iapp/advanced/overview.md

@@ -1,11 +1,11 @@
 ---
-title: Advanced Low-Level iApp Building
+title: Advanced iApp Building
 description:
   Legacy, low-level guides for building confidential iApps (Docker, SGX, TDX,
   SCONE/Gramine, E2E encryption)
 ---
 
-# ⚙️ Advanced Low‑Level iApp Building
+# ⚙️ Advanced iApp Building
 
 ::: warning Important
 

src/guides/build-iapp/index.md

@@ -29,9 +29,9 @@ creating, testing, and deploying confidential iApps.
 - **[Using TDX (Experimental)](/guides/build-iapp/using-tdx)** - Next-gen TEE
   technology
 
-## ⚙️ Advanced Low-Level iApp Building
+## ⚙️ Advanced iApp Building
 
-- **[Advanced Low-Level (legacy guides)](/guides/build-iapp/advanced-low-level/)** -
+- **[Advanced Overview](/guides/build-iapp/advanced/overview)** -
   Deep dive: Docker, SGX/TDX, SCONE/Gramine, datasets & E2E
 
 ## 📚 What's Next?