Mark Task 20 complete and document global exception handlers

Docs/Tasks.md

@@ -348,6 +348,8 @@ Reference: `Docs/Refactoring.md` for full analysis of each issue.
 
 **Docs changes needed:** None.
 
+**Status:** Completed ✅
+
 **Why this is needed:** `__import__()` is an implementation detail of Python's import system and should never appear in application code. It obscures the dependency, bypasses linting checks, and signals that the code was written reactively to solve a circular import that no longer exists.
 
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@@ -385,6 +387,8 @@ Reference: `Docs/Refactoring.md` for full analysis of each issue.
 
 **Docs changes needed:** Update `Docs/Refactoring.md`.
 
+**Status:** Completed ✅
+
 **Why this is needed:** The same try/except→HTTPException conversion is duplicated across every router endpoint. Global handlers reduce boilerplate, make error mapping auditable in one place, and prevent inconsistencies where the same exception produces different status codes in different routes.
 
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