build: global build props and packages config, dev slnf and nuget.config

[damyanpetev]

Description

Added the following global configuration conveniences following modern .NET practices:

• Directory.Build.props/.targets — Repo build customizations; kept deliberately thin (Company/Copyright/Deterministic); per-project settings like TFMs vary too much to hoist safely.
• Directory.Packages.props — Central Package Management (CPM); the per-TFM Microsoft.AspNetCore.Components.Web handled with conditional <PackageVersion> entries. All csprojs stripped of Version= attributes. Note: bunit's floating 1.* is now pinned to 1.40.0.
• templates/Directory.Build.props + Directory.Packages.props — boundary sentinels so the templates subtree (including shipped template content) opts out of repo-wide MSBuild/CPM, keeping it extraction-ready.
• IgniteUI.Blazor.Lite.Library.slnf - convenience solution filter with just the library + unit tests.
• nuget.config — no-op on GitHub-hosted runners; for developer machines to avoid merges with internal feeds configured globally.

Type of Change (check all that apply):

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

Component(s) / Area(s) Affected:

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Test Configuration:

• .NET version:
• Hosting model:
• Browser(s):
• OS:

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 #