feat(templates): add item templates for Ignite UI Blazor components

[dkalinovInfra]

Description

Adds item templates for the individual Ignite UI for Blazor components to the IgniteUI.Blazor.Templates pack, which previously shipped only the igb-blazor project template. Users can now scaffold a ready-to-use component page either from the CLI (dotnet new <igb-component>) or from the Visual Studio Add New Item dialog.

• Added templates/item/** with 43 component templates, each with its .template.config (template.json + ide.host.json + icon.png).
• Each template generates a .razor page with @page routing, a scoped .razor.css, and inline IgniteUI.Blazor.Lite setup instructions in an @code comment (package install, AddIgniteUIBlazor(), _Imports, theme link, render mode).
• In Visual Studio, templates appear under Add New Item → Ignite UI for Blazor\<Group> with per-component icons (via ide.host.json).

Supporting change: to host the item templates alongside the existing project template, the pack layout was reorganized — the project template moved from content/igb-blazor/** to templates/project/igb-blazor/** (pure file moves, no content changes), with IgniteUI.Blazor.Templates.csproj and the READMEs updated to the new templates/ content root.

Motivation / Context

The project template alone gets users a running app, but there is no first-class way to drop a working, conventionally-wired component sample into an existing page. These item templates give a fast, copy-paste-free starting point for each component — discoverable directly from the VS New Item UI (grouped under Ignite UI for Blazor\<Group>), not just the CLI — and the generated code follows the bridge/render-mode conventions of the Lite package.

Type of Change (check all that apply):

• Bug fix
• New functionality
• Refactoring (no functional changes)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog

Component(s) / Area(s) Affected:

IgniteUI.Blazor.Templates — new item-template pack covering 43 components across all groups: Buttons & Actions, Inputs & Forms, Data (Grid), Charts (ApexCharts), Layout, Scheduling/Pickers, Navigation, Notifications, and Data Display. The existing igb-blazor project template is moved (no functional change).

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Installed the pack from source (dotnet new install), scaffolded a Blazor Server app, then generated every item template into the app's Components/Pages and wired each into the nav. The project builds clean (0 warnings, 0 errors) and the pages render and behave correctly at runtime. Verified VS Add New Item grouping/icons via ide.host.json.

Test Configuration:

• .NET version: .NET 10 SDK (templates multi-target net8.0/net9.0/net10.0)
• Hosting model: Blazor Server
• Browser(s): Chrome / Edge
• OS: Windows 11

Screenshots / Recordings

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code
• This PR includes API docs for newly added methods/properties
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes behavioral changes and the feature specification has been updated with them
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

Closes #224