fix(registry): return error on failed name lookup and handle it in delete

[madmecodes]

Closes #840

Two bugs in GetRegistryIdByName:

1. Returns (0, nil) when the registry name isn't found, so callers
   can't distinguish "not found" from success. Fixed to return
   fmt.Errorf("registry '<name>' not found").

2. Calls ListRegistries with empty opts, so the lookup only checks
   the default page. Now passes the name filter so the API handles
   filtering server-side.

Also fixed registry delete to:

• Actually check the error from GetRegistryIdByName instead of
  discarding it with _
• Try strconv.ParseInt first so numeric IDs work as arguments too

Same pattern as the user lookup fix in #820.

[qcserestipy]

This is a duplicate of #841, this will be decided on later.

EDIT: Also please fix linting issues.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 9.00%. Comparing base (60ad0bd) to head (457c646).
⚠️ Report is 146 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/harbor/root/registry/delete.go	0.00%	9 Missing ⚠️
pkg/api/registry_handler.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             main    #851      +/-   ##
=========================================
- Coverage   10.99%   9.00%   -1.99%     
=========================================
  Files         173     272      +99     
  Lines        8671   13449    +4778     
=========================================
+ Hits          953    1211     +258     
- Misses       7612   12123    +4511     
- Partials      106     115       +9     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[madmecodes]

Closing - duplicates #841.