Add browser WebMCP list and invoke commands

[rgarcia]

Summary

• Add browsers webmcp list <id-or-name> with a readable table and raw response output via --json or -o json.
• Add browsers webmcp invoke with a required opaque tool reference, JSON-object input from a flag/file/stdin, and an optional positive timeout. Preserve JSON numbers in input and output.
• Disable SDK retries for every invocation. Preserve the invocation ID when formatting outcome_unknown errors, and return non-zero for API errors, tool errors, and cancellations.
• Document commands, reference lifetime, and ambiguous outcomes. The repo already pins v0.100.0, confirmed as the latest published Go SDK release, so no dependency files changed.

Validation

• go test ./...
• go vet ./...
• Built the CLI and exercised a local HTTP 504 response: one request, exit status 1, empty stdout, and code/invocation ID/message on stderr.
• Command tests cover wiring, ID/name paths, table/raw JSON output, annotations, input sources and validation, timeout serialization, output types, and no retries on 504/500/429 even with retry headers.