fix: refresh DCR provider client on replace

[ankitranjan7]

Description

Fixes DCR provider replacement from the UI by clearing the existing dynamically registered client when a DCR provider is replaced without manual client credentials. The UI now handles DCR replacements with no input fields immediately, instead of redirecting to an empty input form.

Motivation and Context

For DCR OAuth providers like Notion DCR, clicking Replace did not actually replace the stored client because there are no manual client_id / client_secret fields to submit. The existing provider client was preserved, so no change was detected and the old dynamic client kept being reused.

With this change, Replace revokes existing connections and clears the saved DCR client so the next login performs dynamic client registration again.

How Has This Been Tested?

• uv run pytest
• uv run ruff check src/ tests/
• uv run ty check src/
• uv run pre-commit run --all-files

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• All new and existing tests passed.