docs: add guides for agctl installation and request tracing

[Roniscend]

Introduces installation guides for the agctl CLI across Linux, macOS, and Windows platforms. Adds documentation for the agctl trace command, covering TUI usage, request triggering, and JSONL output for debugging.
Fixes: #475

[Copilot]

Pull request overview

Adds new operational documentation for the agctl CLI, including installation/upgrade guidance and a request tracing guide, and links the new tracing workflow from existing debug docs for both standalone and Kubernetes deployment modes.

Changes:

• Adds agctl install/usage pages and agctl trace pages under both standalone and kubernetes docs (for main and latest).
• Introduces shared reusable docs pages for agctl installation and request tracing.
• Updates existing debugging docs to include a new “Trace live requests” section pointing to the new trace guide.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
content/docs/standalone/main/operations/agctl.md	Adds standalone “agctl CLI” page that reuses shared install content.
content/docs/standalone/main/operations/agctl-trace.md	Adds standalone “Trace requests” page that reuses shared trace content.
content/docs/standalone/latest/operations/agctl.md	Adds standalone (latest) “agctl CLI” page that reuses shared install content.
content/docs/standalone/latest/operations/agctl-trace.md	Adds standalone (latest) “Trace requests” page that reuses shared trace content.
content/docs/kubernetes/main/operations/agctl.md	Adds Kubernetes “agctl CLI” page that reuses shared install content.
content/docs/kubernetes/main/operations/agctl-trace.md	Adds Kubernetes “Trace requests” page that reuses shared trace content.
content/docs/kubernetes/latest/operations/agctl.md	Adds Kubernetes (latest) “agctl CLI” page that reuses shared install content.
content/docs/kubernetes/latest/operations/agctl-trace.md	Adds Kubernetes (latest) “Trace requests” page that reuses shared trace content.
assets/agw-docs/pages/operations/debug.md	Links to agctl trace from Kubernetes debug docs via a new “Trace live requests” section.
assets/agw-docs/pages/operations/debug-standalone.md	Links to agctl trace from standalone debug docs via a new “Trace live requests” section.
assets/agw-docs/pages/operations/agctl-trace.md	Adds the shared agctl trace usage guide (TUI, trigger request via --, raw JSONL).
assets/agw-docs/pages/operations/agctl-install.md	Adds the shared agctl install/verify/upgrade guide plus a small command/flag reference.

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[artberger]

Hi @Roniscend , I think that this work conflicts with the agctl docs such as here: https://agentgateway.dev/docs/kubernetes/latest/operations/agctl/

I think parts of your PR might be nice to add, such as the tabs for different OS installations, since right now the docs only cover building from source.

I am not sure if you would prefer to pull in main in this PR, or just close this and open a new one. Apologies for the conflict and inconvenience.