fix: keep navigation on single-character cluster details

[lixd]

/kind bug
/kind regression

What this PR does / why we need it:

Fixes the cluster-detail menu route matcher so single-character cluster IDs keep the left navigation visible.

Which issue(s) this PR fixes:

Fixes #

Special notes for reviewers:

The previous pattern required at least two characters after /cluster/, so /cluster/c did not match and the menu rendered nothing.

Does this PR introduced a user-facing change?

Fix missing left navigation on cluster detail pages whose cluster ID has one character.

Additional documentation, usage docs, etc.:

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[lixd]

/lgtm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 47.30%. Comparing base (c8ec5fe) to head (784adfb).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #430   +/-   ##
=======================================
  Coverage   47.30%   47.30%           
=======================================
  Files           7        7           
  Lines         613      613           
  Branches      176      176           
=======================================
  Hits          290      290           
  Misses        250      250           
  Partials       73       73           

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