feat: Add dismissible warning UI for threshold loading errors

- Replace console.warn with visible MessageBar warning when map color thresholds fail to load
- Add DismissRegular icon button to allow users to dismiss the warning
- Add dismissedThresholdWarning state to manage warning visibility
- Add mock and test for useMapColorThresholds hook
- Add test case verifying warning displays and can be dismissed
- Remove TASK-QUALITY-04 from Tasks.md (completed)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Docs/Tasks.md

@@ -1,22 +1,3 @@
-### TASK-QUALITY-04 — `pendingSaveRef as boolean` Redundant Cast in `useAutoSave`
-
-**Where found**
-`frontend/src/hooks/useAutoSave.ts`. The code contains `if (pendingSaveRef.current as boolean)` where `pendingSaveRef` is already typed as `React.MutableRefObject<boolean>`. The `as boolean` cast is redundant and suggests the author was uncertain about the type.
-
-**Goal**
-Remove the cast: `if (pendingSaveRef.current)`. Run TypeScript type-check to confirm no error is introduced.
-
-**Possible traps and issues**
-- None. This is a one-line cleanup.
-
-**Docs changes needed**
-None required.
-
-**Why this is needed**
-Redundant type assertions are noise that makes reviewers second-guess the type system. They also suppress TypeScript errors in cases where the cast is actually incorrect.
-
----
-
 ### TASK-QUALITY-05 — `console.warn` in `MapPage` Provides No User Feedback for Threshold Errors
 
 **Where found**