feat(cli): rich login/logout UX

[spomichter]

Polishes the dimos login / dimos logout experience on top of #3522, using rich (already a typer dependency — no new deps):

• login: cyan panel with verification URL + device code chip, live spinner with mm:ss countdown while polling, gradient DIMOS wordmark + green confirmation on success
• logout: styled ⏻ Logged out. line with dimmed revoke URL
• whoami: same text, bold email / dim scopes

rich degrades to plain text when stdout isn't a TTY, so robot and CI logs stay clean. Existing tests pass unchanged; mypy clean.

[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
dimos/cli/cloud.py	96.42%	0 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main    #3523      +/-   ##
==========================================
- Coverage   76.06%   76.06%   -0.01%     
==========================================
  Files        1226     1226              
  Lines      118922   118936      +14     
  Branches    10666    10667       +1     
==========================================
+ Hits        90463    90473      +10     
- Misses      25381    25383       +2     
- Partials     3078     3080       +2     

Flag	Coverage Δ
OS-ubuntu-24.04-arm	70.47% <96.42%> (+<0.01%)	⬆️
OS-ubuntu-latest	72.25% <96.42%> (-0.01%)	⬇️
Py-3.10	72.25% <96.42%> (+<0.01%)	⬆️
Py-3.11	72.24% <96.42%> (-0.01%)	⬇️
Py-3.12	72.25% <96.42%> (+<0.01%)	⬆️
Py-3.13	72.25% <96.42%> (+<0.01%)	⬆️
Py-3.14	72.25% <96.42%> (+<0.01%)	⬆️
Py-3.14t	72.25% <96.42%> (+<0.01%)	⬆️
SelfHosted-Large	29.76% <25.00%> (+<0.01%)	⬆️
SelfHosted-Linux	35.83% <25.00%> (+<0.01%)	⬆️

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Files with missing lines	Coverage Δ
dimos/cli/cloud.py	87.03% <96.42%> (+1.93%)	⬆️

... and 2 files with indirect coverage changes

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