docs(agents): add AGENTS.md, knowledge base, and Copilot context

[antsukanova]

Description

• Give contributors and AI tools a single place to learn commands, review priorities, and repo conventions (AGENTS.md, scoped instructions, Git conventions).
• Add a short knowledge-base overview of the package areas and CapabilityState.
• Keep hand-written contributor docs separate from generated API docs so yarn docs cannot delete them.
• Align pull-request CI with the documented local checks (Prettier, spelling, TypeScript validation, build).

Testing

No manual browser testing was needed. This change does not modify runtime behavior or the public API.

PR description templates working fine.

This change implements...

• A new feature
• A bug fix
• Other (please specify): AI-assisted development documentation and tooling

Is this a breaking change?

• Yes
• No

I certify that...

• All relevant unit and integration tests have passed and/or have been updated according to this change.

Generative AI (GAI) Usage Disclosure

Reference: Cisco GAI Coding Guidelines

• Cisco approved GAI tool/IDE was used for coding - eg: VSCode, Cursor, Windsurf, Codex, Claude code
• No GAI - Code was written entirely manually without GAI assistance

If a GAI tool/IDE was used then select the category that best describes GAI usage in this PR:

• Manual Draft with GAI Refinement - I/we created a draft manually that was non-substantively modified by GAI (e.g., refactoring was performed by GAI on manually written code) (Default)
• GAI Draft with Manual Customization - GAI tool was used to create a draft that I/we subsequently customized or modified.
• GAI Generated Code - Code was generated entirely by GAI

Additional GAI Usage Details (Optional):

[BlueLamantine]

One small gap: this PR turns markdown formatting and spelling into a hard CI gate, but there's nothing catching it locally. lint-staged only looks at *.ts, so if you edit AGENTS.md or a knowledge-base article you get no feedback at all until CI comes back red. Since the whole point of the PR is to line CI up with the documented local checks, it seemed worth closing the loop in the other direction as well.

In lint-staged:

"{docs/**/*.md,AGENTS.md,README.md,.github/**/*.md}": ["prettier --write", "cspell"]

WDYT ?