fix: address santa-loop review findings (round 2)

Stage and commit remaining 4 title renames that were left as
unstaged working-tree changes:
- API.md: Languard Server Manager → Languard Servers Manager
- DATABASE.md: Languard Server Manager → Languard Servers Manager
- MODULES.md: Languard Server Manager → Languard Servers Manager
- THREADING.md: Languard Server Manager → Languard Servers Manager

API.md

@@ -1,4 +1,4 @@
-# Languard Server Manager — API Contract
+# Languard Servers Manager — API Contract
 
 ## Base URL
 ```

DATABASE.md

@@ -1,4 +1,4 @@
-# Languard Server Manager — Database Design
+# Languard Servers Manager — Database Design
 
 ## Engine
 - **SQLite** via `SQLAlchemy Core` (sync for all access — routes and threads)

MODULES.md

@@ -1,4 +1,4 @@
-# Languard Server Manager — Python Module Breakdown
+# Languard Servers Manager — Python Module Breakdown
 
 ## Project Structure
 

THREADING.md

@@ -1,4 +1,4 @@
-# Languard Server Manager — Threading & Concurrency Design
+# Languard Servers Manager — Threading & Concurrency Design
 
 ## Overview