Initial repository scaffold: solution, packages, demo host, licensing, persistence, Tabler components, tests and CI

[Code-311]

Motivation

• Establish a Phase‑0 baseline for the Code311 multi‑package UI framework with consistent repository governance and build defaults.
• Enforce quality gates (nullable, analyzers, XML docs, deterministic builds, central package versions, SDK pinning) at repository root.
• Provide a runnable hybrid demo host and first‑class packages for Tabler adapters, core abstractions, licensing and EF Core persistence.
• Add CI and an initial automated test matrix to validate core integration and mapping behaviors.

Description

• Added solution and repo tooling: Code311.sln, global.json, Directory.Build.props, Directory.Build.targets, and Directory.Packages.props to centralize SDK, analyzer and package settings.
• Introduced package projects and implementations for framework layering: Code311.Ui.Abstractions, Code311.Ui.Core, Code311.Tabler.Core, Code311.Tabler.Components, Code311.Tabler.Mvc, Code311.Tabler.Razor, Code311.Tabler.Dashboard, Code311.Tabler.Widgets.*, Code311.Persistence.EFCore, and Code311.Licensing, with DI registration helpers and mapping/theming/asset contracts.
• Added demo host Code311.Host including controllers, Razor page, views, services (preferences, demo user context), startup wiring, and an in‑memory demo license provider for runtime feature gating.
• Added comprehensive test projects under tests/ covering unit and integration tests for licensing, persistence, Tabler core/components/dashboard/widgets, MVC/Razor adapters and abstraction contracts, and added a GitHub Actions ci workflow that restores, builds and runs dotnet test Code311.sln.

Testing

• No automated test run was executed as part of this PR; the repository contains a full test matrix that can be executed locally or in CI.
• To run the test suite locally use dotnet test Code311.sln.
• The commit adds many focused unit and integration tests (under tests/) that exercise licensing validation, EF Core preference store, Tabler mappings, component/taghelper rendering, widget slot behaviors and MVC/Razor adapter filters.

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Codex Task