Show notifications on registration failure

[lasuillard]

Display a toast notification if the OAuth application registration is unsuccessful.

Additionally, implement the following features:

• Enable users to manually input an access token, allowing the use of a test token and eliminating the necessity for OAuth app registration.
• Eliminate the unattractive focus outline around the menu icon when it is clicked.

Resolves #28 and fixes #38.

[codecov]

Codecov Report

Attention: Patch coverage is 72.64151% with 29 lines in your changes missing coverage. Please review.

Project coverage is 69.20%. Comparing base (7fe03ef) to head (74cfcae).
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/lib/messages.ts	68.75%	14 Missing and 1 partial ⚠️
src/pages/options/Page.svelte	0.00%	13 Missing ⚠️
src/components/Message.svelte	97.61%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #51      +/-   ##
==========================================
+ Coverage   68.57%   69.20%   +0.63%     
==========================================
  Files          19       21       +2     
  Lines         910     1010     +100     
  Branches       58       60       +2     
==========================================
+ Hits          624      699      +75     
- Misses        233      256      +23     
- Partials       53       55       +2     

Flag	Coverage Δ
unit	69.20% <72.64%> (+0.63%)	⬆️

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