Replace samples with examples and add ASP.NET Core project

[rohit-fastpix]

FastPix C# SDK - Documentation PR

Documentation Changes

What Changed

• New documentation added
• Existing documentation updated
• Documentation errors fixed
• Code examples updated
• Links and references updated
• Other — renamed samples/ → examples/, added a runnable ASP.NET Core project

Files Modified

• README.md
• docs/ files
• USAGE.md
• CONTRIBUTING.md
• Other: examples/ (new folder, replaces samples/) — example programs, AspNetCore/ project, README.md, .env.example, .gitignore

Summary

Brief description of changes:

Replaced the old samples/ folder with a runnable examples/ project. The previous
samples referenced an API that doesn't exist (FastPix.Builder(), Security.AccessToken,
client.Videos.Upload) and wouldn't compile. Every example is rewritten against the
real SDK and run via `dotnet run -- <name>`:

  create-upload, verify-webhook (offline), sdk-init, video-management,
  playback, live-streaming, ai-features, playlist, error-handling

Added examples/AspNetCore/ — a minimal web integration with two endpoints:
POST /uploads (mints a signed upload URL) and POST /webhooks (verifies the
FastPix-Signature on the raw body, then dispatches the event). Each area has a
README, .env.example, and env-var-based credentials (no secrets in code).

Code Examples (if Applicable)

// Construct the client, then mint a signed direct-upload URL.
// The client PUTs the file straight to that URL — bytes never touch your server.
using Fastpix;
using Fastpix.Models.Components;
using Fastpix.Models.Requests;

var sdk = new FastpixSDK(security: new Security
{
    Username = Environment.GetEnvironmentVariable("FASTPIX_USERNAME"),
    Password = Environment.GetEnvironmentVariable("FASTPIX_PASSWORD"),
});

var res = await sdk.InputVideo.UploadAsync(new DirectUploadVideoMediaRequest
{
    CorsOrigin = "*", // tighten for production
    PushMediaSettings = new PushMediaSettings(),
});

var upload = res.Object?.Data;
Console.WriteLine($"uploadId: {upload?.UploadId}");
Console.WriteLine($"url:      {upload?.Url}");

Testing

• All code examples tested — built with 0 warnings; live-verified against api.fastpix.com. Real end-to-end upload confirmed (mint URL → PUT a 42,953-byte mp4 → HTTP 200, x-goog-stored-content-length: 42953) for both the CLI example and the ASP.NET /uploads endpoint.
• Links verified
• Grammar checked
• Formatting consistent

Review Checklist

• Content is accurate
• Code examples work
• Links are working
• Grammar is correct
• Formatting is consistent

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Ready for review!