fix: Adjust welcome and end screen

[esterlus]

Fixes #61
Fixes #67

[Copilot]

Pull request overview

Updates the onboarding flow to remove the (currently non-functional) anonymous path and to show a dedicated end-of-onboarding thank-you message after feedback submission, aligning the UI with Issues #61 and #67. It also adds Nix/direnv developer environment files and updates ignore rules.

Changes:

• Remove the “Stay anonymous” option from the login screen and adjust onboarding privacy copy.
• Add a “Thank you” dialog shown after submitting the final feedback step instead of immediately returning to login.
• Add Nix flake + direnv config for a reproducible dev shell; update .gitignore accordingly (and refresh yarn.lock).

Reviewed changes

Copilot reviewed 4 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/views/Login.tsx	Removes anonymous path button; updates onboarding/privacy messaging and login CTA.
src/views/onboarding/99_Feedback.tsx	Adds thank-you dialog flow after “The End” submission.
flake.nix	Introduces a Nix flake-based dev shell for the project.
flake.lock	Pins nixpkgs revision for the flake.
.envrc	Enables direnv to load the flake dev shell automatically.
.gitignore	Ignores .direnv directory.
yarn.lock	Updates lockfile with additional/changed transitive dependencies.

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