test: coverage improvements, flaky fix, and dead test cleanup

[jongio]

Summary

Addresses 8 test improvement issues in a single PR:

• test(orchestrator): remove placeholder timeout test file #186: Remove placeholder timeout test (orchestrator_timeout_test.go deleted)
• test(azure): implement skipped diagnostics tests or remove dead scaffolding #187: Remove dead diagnostics test scaffolding (3 skipped tests + unused mock type removed)
• test(service): add unit tests for parser.go and graph.go dependency resolution #206: Add unit tests for graph.go and parser.go (dependency graph, cycle detection, topological sort, service filtering)
• test(dashboard): Go backend package at 25% coverage with 23 untested files #237: Add dashboard backend unit tests (security headers, payload construction, YAML loading, timeout context)
• test(dashboard): frontend has no coverage thresholds and 54% of files untested #238: Add coverage thresholds to vitest config (40% for statements/branches/functions/lines)
• test(docker): exec.go has zero test coverage for all Docker CLI operations #239: Already addressed by existing thorough test suite in client_test.go
• test(commands): service lifecycle commands (start/stop/restart) lack test coverage #240: Add service lifecycle command tests (parseServiceList, isRunning, isStopped, newErrorResult)
• test(flaky): replace time.Sleep-based test synchronization with event-driven coordination #241: Fix flaky time.Sleep-based test synchronization (replaced with polling loops + buffered channel/select patterns)

Changes

Deleted

• cli/src/internal/orchestrator/orchestrator_timeout_test.go: placeholder with only .Skip

Modified

• cli/src/internal/azure/diagnostics_test.go: removed 3 dead test functions that were always skipped
• cli/src/cmd/app/commands/logs_follow_test.go: replaced all time.Sleep patterns with deterministic synchronization
• cli/dashboard/vitest.config.ts: added coverage thresholds

Created

• cli/src/internal/service/graph_test.go: 12 table-driven tests for dependency graph operations
• cli/src/internal/service/parser_test.go: tests for FilterServices, HasServices, GetServiceProjectDir
• cli/src/cmd/app/commands/service_control_test.go: tests for parseServiceList, isRunning, isStopped, newErrorResult
• cli/src/internal/dashboard/dashboard_test.go: tests for securityHeaders, serviceInfoPayload, loadAzureYaml, timeoutContext

Testing

All new and modified tests pass locally. The two pre-existing failures (TestRunFunctionApp_WithHostJson, TestContainerRuntimeDetection) are environment-dependent and unrelated to these changes.

Closes #186, #187, #206, #237, #238, #240, #241
Relates to #239 (already covered)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.03%. Comparing base (8735f89) to head (016033f).
⚠️ Report is 16 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #250      +/-   ##
==========================================
- Coverage   57.06%   57.03%   -0.03%     
==========================================
  Files         158      156       -2     
  Lines       22736    22708      -28     
==========================================
- Hits        12974    12952      -22     
+ Misses       8963     8952      -11     
- Partials      799      804       +5     

Flag	Coverage Δ
unittests	57.03% <ø> (-0.03%)	⬇️

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see 20 files with indirect coverage changes

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