Add browser-based auth flow

[itssimon]

Summary by cubic

Adds a browser-based auth flow to the CLI that opens the Apitally dashboard, lets the user select a team, and returns a newly created API key to save in ~/.apitally/auth.json. Aligns with DEV-103 by using the dashboard for team selection and creating a CLI-specific key, with a fallback to paste a key when running interactively.

• New Features

  • Opens https://app.apitally.io/cli-auth?callback_port=<port> and runs a localhost callback server to receive { api_key } via JSON POST; includes CORS support and a 5-minute timeout.
  • Fallback: users can paste an API key in an interactive terminal; --api-key still saves directly without opening the browser.
  • Validates API key format before saving and prints colored success/error output when supported.
  • Hidden --app-url flag (APITALLY_APP_URL) to target other environments.
  • Updated CLI docs; added tests for callback handling and key validation.

• Dependencies

  • Added open (launch default browser) and regex (API key validation).

^{Written for commit a5e9206. Summary will update on new commits.}

[sentry]

Codecov Report

❌ Patch coverage is 90.60403% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.26%. Comparing base (a3c4f76) to head (a5e9206).

Files with missing lines	Patch %	Lines
src/main.rs	0.00%	7 Missing ⚠️
src/auth.rs	95.62%	6 Missing ⚠️
src/utils.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
+ Coverage   90.80%   91.26%   +0.45%     
==========================================
  Files          12       12              
  Lines        1817     1934     +117     
==========================================
+ Hits         1650     1765     +115     
- Misses        167      169       +2     

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