Fix compliance findings in Frends.Pdf.Create (FT0007, FT0011, FT0014, FT0015, FT0018)

[Copilot]

Resolves 18 FrendsTaskAnalyzer findings in Frends.Pdf.Create by aligning the task with current platform standards.

Breaking changes (→ v3.0.0)

Method signature — the three separate [PropertyTab] parameters (FileProperties, DocumentSettings, DocumentContent) were not recognized platform types (FT0018) and Input/CancellationToken were missing (FT0007). They are now consolidated:

// Before
public static Result Create(
    [PropertyTab] FileProperties outputFile,
    [PropertyTab] DocumentSettings documentSettings,
    [PropertyTab] DocumentContent content,
    [PropertyTab] Options options)

// After
public static Result Create(
    [PropertyTab] Input input,
    [PropertyTab] Options options,
    CancellationToken cancellationToken)

Input groups the three former parameters as OutputFile, DocumentSettings, and Content.

Non-breaking additions

• Options.ErrorMessageOnFailure (FT0015) — allows overriding the thrown/returned error message.
• Result.Error (FT0011) — populated with message and inner exception when ThrowErrorOnFailure = false.
• Helpers/ErrorHandler — standard platform pattern; all exceptions in Create() now route through exception.Handle(options) instead of hand-rolled if (ThrowErrorOnFailure) throw.
• XML docs — added <summary> and <example> to all flagged properties/methods in FontMetadata, Extensions, and FileFontResolver (FT0014).

Project / tooling

• FrendsTaskMetadata.json changed from <None> to <AdditionalFiles> (required by FrendsTaskAnalyzers for FT0020).
• Added StyleCop.Analyzers and FrendsTaskAnalyzers package references; added GlobalSuppressions.cs with standard Frends suppressions.

Tests

• Existing tests updated to the new Input-based call site.
• Tests that asserted FileNotFoundException updated to Exception — the ErrorHandler wraps all exceptions in new Exception(message, innerEx).
• ErrorHandlerTest added covering: throw on failure, return failed result, custom error message (throw and return paths).

[MatteoDelOmbra]

@copilot go through comments and resolve them accordingly