Refactor plan parsing, rendering, and web endpoints for maintainability

[MasayukiOzawa]

Summary

• Split parsing and XML traversal logic into smaller focused components for easier maintenance.
• Refined plan rendering services to isolate layout, critical path, and SVG generation concerns.
• Simplified web app wiring and endpoint/services around estimated showplan handling, export, and workspace state.
• Added/updated tests around PlanWorkspaceService behavior.

Testing

• Updated unit coverage for workspace state handling.
• Not run (not requested).

[Copilot]

Pull request overview

This PR refactors the showplan parsing/rendering pipeline and the web layer by extracting endpoint and UI workspace logic into focused helper/services, aiming to improve maintainability and reduce duplicated orchestration code in pages/endpoints.

Changes:

• Introduces PlanWorkspaceService and migrates Home page plan/statement/compare orchestration to it, adding unit tests.
• Extracts plan export and estimated-showplan endpoint logic into PlanExportService and EstimatedShowplanApiService.
• Splits previously-inline parser/rendering helpers into dedicated components (XML loading/schema version resolution, attribute-path matching, critical-path finding, SVG edge path building).

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/MSSQLPlanViewer.Core.Tests/PlanWorkspaceServiceTests.cs	Adds coverage for PlanWorkspaceService plan initialization, statement selection, and compare selection.
src/MSSQLPlanViewer.Web/State/PlanWorkspaceService.cs	New service encapsulating loaded-plan workspace state transitions (select statement, refresh layout, compare selection).
src/MSSQLPlanViewer.Web/Program.cs	Registers new web-layer services in DI.
src/MSSQLPlanViewer.Web/PlanExportService.cs	New service encapsulating export request validation, statement resolution, and file responses.
src/MSSQLPlanViewer.Web/PlanExportEndpoints.cs	Refactors endpoints to delegate export execution to PlanExportService and centralizes OpenAPI helpers usage.
src/MSSQLPlanViewer.Web/OpenApiDocumentationHelpers.cs	New shared OpenAPI request-body/schema documentation helper methods.
src/MSSQLPlanViewer.Web/EstimatedShowplanEndpoints.cs	Refactors endpoint to delegate execution to EstimatedShowplanApiService and centralizes OpenAPI helpers usage.
src/MSSQLPlanViewer.Web/EstimatedShowplanApiService.cs	New service encapsulating estimated-showplan validation, provider call, parsing, and response shaping.
src/MSSQLPlanViewer.Web/Components/Pages/Home.razor.cs	Simplifies page orchestration by delegating to PlanWorkspaceService.
src/MSSQLPlanViewer.Web/Components/Pages/Home.razor	Updates DI usage to inject PlanWorkspaceService instead of multiple lower-level services.
src/MSSQLPlanViewer.Core/Rendering/PlanGraphSvgRenderer.cs	Delegates SVG edge-path generation to new builder helper.
src/MSSQLPlanViewer.Core/Rendering/PlanGraphSvgPathBuilder.cs	New helper for consistent SVG path construction (horizontal vs vertical).
src/MSSQLPlanViewer.Core/Rendering/PlanGraphLayoutService.cs	Delegates critical path computation to a dedicated helper.
src/MSSQLPlanViewer.Core/Rendering/PlanGraphCriticalPathFinder.cs	New helper encapsulating critical-path tracing logic.
src/MSSQLPlanViewer.Core/Parsing/ShowplanXmlElement.cs	New XML helper for element name/attribute retrieval.
src/MSSQLPlanViewer.Core/Parsing/ShowplanXmlDocumentLoader.cs	New XML loader enforcing safe reader settings and document size limits.
src/MSSQLPlanViewer.Core/Parsing/ShowplanXmlAttributePathMatcher.cs	New helper encapsulating attribute-path wildcard matching logic.
src/MSSQLPlanViewer.Core/Parsing/ShowplanSchemaVersionResolver.cs	New helper mapping showplan XML namespace URIs to schema versions.
src/MSSQLPlanViewer.Core/Parsing/ShowplanParser.cs	Updates parser to use new loader/schema resolver and new attribute-path matcher.