fix: suppress retry logs in version command when SpiceDB unavailable

[ivanauth]

Summary

Fixes #554

When running zed version with an unavailable SpiceDB instance, the command would retry multiple times and log noisy error messages that cluttered the output.

Changes

• Disables retries by default for the version command (sets max-retries=0)
• Respects user-specified --max-retries if explicitly set
• Restores both flag value and Changed state to preserve flag semantics
• Logs connection failures at debug level instead of error
• Always prints service: (unknown) for consistent output format
• Adds test coverage for unavailable server scenario

Before

$ zed version --endpoint=localhost:12345 --insecure
client: zed v0.33.0
{"level":"error","error":"rpc error: code = Unavailable...","attempt":1,...}
{"level":"error","error":"rpc error: code = Unavailable...","attempt":2,...}
{"level":"error","error":"rpc error: code = Unavailable...","attempt":3,...}
... (9+ retry logs)
service: (unknown)

After

$ zed version --endpoint=localhost:12345 --insecure
client: zed v0.33.0
service: (unknown)

Test Plan

• All existing tests pass
• Added TestVersionCommandWithUnavailableServer to verify silent fallback
• Manually tested with unavailable endpoint (no retry logs)
• Verified user-specified --max-retries is still respected

[codecov-commenter]

Codecov Report

❌ Patch coverage is 67.85714% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.64%. Comparing base (7ed5ab0) to head (72b70ad).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/cmd/version.go	67.85%	8 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #564      +/-   ##
==========================================
+ Coverage   39.28%   40.64%   +1.36%     
==========================================
  Files          37       37              
  Lines        5448     5494      +46     
==========================================
+ Hits         2140     2233      +93     
+ Misses       3063     3009      -54     
- Partials      245      252       +7     

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