Make --aggregate default for nuget command, enhance tool packaging, add documentation

[Copilot]

Changes the nuget command to aggregate packages by default (more useful view), improves .NET tool packaging metadata, and adds comprehensive documentation.

Changes

• nuget command defaults

  • --aggregate now defaults to true
  • Added --no-aggregate flag to opt-out

• Tool packaging

  • Added PackageReadmeFile, RepositoryUrl, RepositoryType
  • Expanded PackageTags for discoverability
  • Shortened Description to avoid truncation

• Documentation

  • README.md: Full command reference, installation, how-it-works sections
  • README_FUN.md: Same content, lighter tone

Usage

# Aggregated view (now default)
bld nuget --root /path/to/repo

# Per-project view (opt-out)
bld nuget --root /path/to/repo --no-aggregate

Original prompt

for the bld nuget, make the --aggregate option the default
go over the source code and improve, optimize, enhance and ensure the quality of the code
create two readme.md. One should be informational, show examples and explain how the tool works under the hood. the second one should do the same but in a more light-hearted, self deprecating manner. Not strong tone, just a touch.

also enable the tool to be packaged as .NET tool

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