fix: fix accessing atest web pages err

[yuluo-yx]

• Fixed Running via Docker results in an error when accessing the web page. #871

[sonarqubecloud]

Quality Gate failed

Failed conditions
16.2% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud

[github-actions]

There are 1 test cases, failed count 0:

Name	Average	Max	Min	Count	Error
	12.435905ms	14.191651ms	10.656783ms	3	0

Reported by api-testing.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

🟢 Metrics 5 complexity

Metric	Results
Complexity	✅ 5 (≤ 20 complexity)

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_{TIP This summary will be updated as you push new changes. Give us feedback}

[LinuxSuRen]

Approve ✅ — verified locally and via CI.

Root cause & fix are correct. On a fresh install without data/core/extension.yaml, GetStoreKinds propagated the os.ReadFile error, which made the GetStores/GetStoreKinds RPCs fail and broke the web console. Treating only os.IsNotExist as "no extensions configured" (while still surfacing permission errors and YAML parse errors) is the right behavior.

Verification

• Ran go test ./pkg/testing/ on this branch locally: all pass, including the two new subtests.
• CI at head is green (Build / Test / E2E / BuildEmbedUI / BuildDesktop on all OSes).
• The go.sum cleanup is fine: go.mod pins linuxsuren/go-service v0.0.2; the removed pseudo-version entry was stale.
• New coverage at both levels (unit store_test.go + server-level remote_server_test.go) — nice.

Non-blocking nits

• Consider errors.Is(err, fs.ErrNotExist) instead of os.IsNotExist for modern style.
• getRemoteServerInTempDirWithoutExtensions duplicates most of getRemoteServerInTempDir; could share a helper with a flag.
• SonarCloud quality gate is red (coverage on new code) — not blocking from my side.