[Update] use the short SPDX form for the licence in source headers; fixes #103

[samatstariongroup]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the ReqIFSharp code style guidelines
• I have provided test coverage for my change (where applicable)

Description

Fixes #103.

The 17-line Apache-2.0 notice at the top of every C# source file is replaced by the short SPDX form, inside the existing <copyright> block:

// -------------------------------------------------------------------------------------------------
// <copyright file="ReqIF.cs" company="Starion Group S.A.">
//
//   SPDX-FileCopyrightText: 2017-2026 Starion Group S.A.
//   SPDX-License-Identifier: Apache-2.0
//
// </copyright>
// ------------------------------------------------------------------------------------------------

The licence itself does not change: the full text stays in LICENSE, and the packages keep PackageLicenseExpression Apache-2.0.

Changes

• All 145 .cs files: only the header comment changed (every changed line is a // comment, within the old 19-line header); BOMs are kept. Headers with an extra space of indentation are normalized.
• Three headers named another file; they now name their own file: EmbeddedValueTestFixture.cs (was AttributeValueXHTMLTestFixture.cs), ReqIfPropertyAttributeTestFixture.cs (was PropertyAttributeTestFixture.cs) and AlternativeID.cs (was AlternativeId.cs).
• ReqIFSharp.sln.DotSettings: the ReSharper file-header template produces the short form for new files (it also said 2017-2025).
• NOTICE: 2014-2026 → 2017-2026, the range of the headers and Directory.Build.props (the first commit is from 2017).
• CLAUDE.md: the header convention describes the short form.
• CHANGELOG.md: entry under [Unreleased] → Changed.

Decisions (from the open points in the issue)

• The <copyright file=... company=...> block is kept around the SPDX lines.
• One year range everywhere: 2017-2026.
• No REUSE configuration (REUSE.toml) or REUSE check in CI in this change; it can be a follow-up.

Verification

• git grep "Licensed under the Apache License" finds only LICENSE and NOTICE; every .cs file has SPDX-FileCopyrightText and SPDX-License-Identifier.
• dotnet build -c Release: 0 warnings; dotnet test: 620 passed.

🤖 Generated with Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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