Preserve keeplist prefix case in UI validation

[Therosin]

Motivation

• Align UI prefix handling with core logic by preserving the exact user-entered keeplist prefix casing while retaining existing validation constraints.

Description

• Stop lowercasing input in applyPrefixValue (removed .toLowerCase()), validate the trimmed value against /^[A-Za-z0-9_-]+$/, and assign keeplistPrefix = trimmed so the active keeplist label reflects the user-entered case in main.ts.
• Add a regression assertion to logic_test.ts to ensure resolveKeeplistName preserves mixed-case prefixes (e.g., Vanilla_Profile).

Testing

• Formatted files with deno fmt main.ts logic_test.ts which completed successfully.
• Ran the test suite with deno task test and all 58 tests passed.

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Codex Task

[Copilot]

Pull request overview

This PR aligns the UI keeplist prefix handling in main.ts with the existing mixed-case support already present in the core logic.ts. Previously, applyPrefixValue lowercased the user's input before storing it, causing the active keeplist name shown in the UI and passed to core functions to always be lowercase, even though logic.ts (via validateKeeplistName and isProtectedKeeplistPath) already accepted and operated on mixed-case prefixes.

Changes:

• Removed .toLowerCase() normalization in applyPrefixValue, updated the validation regex from [a-z0-9_-] to [A-Za-z0-9_-], and now stores the trimmed (not lowercased) value as keeplistPrefix.
• Added a regression test in logic_test.ts to assert that resolveKeeplistName("Vanilla_Profile") returns "#Vanilla_Profile-keeplist.txt", confirming mixed-case prefix preservation end-to-end.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
main.ts	Removes lowercase normalization in applyPrefixValue; updates validation regex to allow uppercase letters; stores the user-entered case directly.
logic_test.ts	Adds a mixed-case assertion to the existing resolveKeeplistName test to cover the preserved-case behavior.

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