Make core packages compliant with Microsoft NuGet authoring requirements

[singhk97]

Summary

• Brings the three core packages (Microsoft.Teams.Core, Microsoft.Teams.Apps, Microsoft.Teams.Apps.BotBuilder) into compliance with the Microsoft NuGet package authoring requirements.
• Adds PackageProjectUrl, fixes a broken PackageIcon packing path in core/src/Directory.Build.props, renames Description → PackageDescription, adds PackageTags, and adds MIT license/copyright header comments to each csproj.
• Also bumps versionHeightOffset in core/version.json and core/src/Microsoft.Teams.Apps/version.json.

Compliance gaps addressed

Requirement	Before	After
PackageProjectUrl	missing	https://microsoft.github.io/teams-sdk
PackageIcon packing	broken path ((MSBuildThisFileDirectory)../../../../bot_icon.png)	$(MSBuildThisFileDirectory)../bot_icon.png
PackageDescription	used Description	PackageDescription
PackageTags	missing	microsoft;teams;msteams;copilot;ai;adaptive-cards;apps;bots
License header	missing	MIT header comment in each csproj

Known follow-up (not in this PR)

• core/bot_icon.png is 75x75; the authoring spec recommends 100x100 (with clean downscaling to 32/48/64/128).
• Strong-name signing (SignAssembly + key.snk) — not adopted in core yet, matches existing core stance.

Test plan

• dotnet pack the three core projects locally and inspect the produced .nupkg to confirm bot_icon.png and README.md are packed at the root and the metadata fields render correctly.
• Verify the icon shows up on the nuget.org preview / nuget.exe verify step in CI.
• CI build passes on the branch.

[Copilot]

Pull request overview

Brings the three core NuGet packages into compliance with Microsoft's NuGet authoring requirements by adding required metadata, fixing the broken PackageIcon packing path, and adding MIT license header comments to each csproj. Also bumps version height offsets so package versions remain stable across the new commits.

Changes:

• Add PackageProjectUrl, PackageTags, MIT/copyright header comments, and rename Description → PackageDescription for the three core packages.
• Fix the bot_icon.png packing path in core/src/Directory.Build.props (previously a literal (MSBuildThisFileDirectory) token with too many ../ segments).
• Bump versionHeightOffset in core/version.json and core/src/Microsoft.Teams.Apps/version.json to absorb the new commits.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
core/version.json	Decrement versionHeightOffset from -3 to -6 to keep version stable across new commits.
core/src/Microsoft.Teams.Apps/version.json	Add versionHeightOffset: -3 for the Apps package.
core/src/Directory.Build.props	Add PackageProjectUrl; fix PackageIcon None Include path to use $(MSBuildThisFileDirectory)../bot_icon.png.
core/src/Microsoft.Teams.Core/Microsoft.Teams.Core.csproj	Add MIT header, rename Description → PackageDescription, add PackageTags.
core/src/Microsoft.Teams.Apps/Microsoft.Teams.Apps.csproj	Same metadata cleanup as above.
core/src/Microsoft.Teams.Apps.BotBuilder/Microsoft.Teams.Apps.BotBuilder.csproj	Same metadata cleanup as above.

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