feat(cli): add --skill-id option and replace --json with --format json

[devin-ai-integration]

Summary

Two CLI changes to the vlmrun chat command:

1. --skill-id: New repeatable option for referencing server-side skills as <skill-name>:<version> (e.g. my-skill:latest, my-skill:3). If no version is provided, defaults to latest. Mutually exclusive with --skill (inline skill directories).

2. --format json replaces --json/-j: Output format is now specified via --format/-f with json as the only currently supported value. This is a breaking change — the old --json flag is removed with no backward-compatible alias.

Help text and examples updated to document both changes.

Review & Testing Checklist for Human

• Breaking change acknowledgment: --json / -j is fully removed. Any existing scripts, CI pipelines, or docs referencing vlmrun chat --json will break. Verify this is intentional and no deprecation period is needed.
• No tests for --skill-id parsing logic: The <name>:<version> splitting (rsplit(":", 1)) and the fallback to version="latest" when no colon is present have no dedicated unit tests. Consider whether edge cases (empty name, empty version like skill:, multiple colons) need coverage.
• No test for mutual exclusivity: Passing both --skill and --skill-id should error, but this path is untested.
• Manual test: Run vlmrun chat "hello" --skill-id my-skill:latest and vlmrun chat "hello" --format json --no-stream to verify both features work end-to-end against the API.

Notes

• The --format option is a string rather than an enum, so it's extensible for future formats (e.g. yaml, csv) but currently only accepts json (case-insensitive).
• Skill ID references are constructed as AgentSkill(type="skill_reference", skill_id=<name>, version=<version>) and serialized into the extra_body.skills payload, same path as inline skills.

Link to Devin session: https://app.devin.ai/sessions/d40920dcf04246b7af4636b4fa6f5a65
Requested by: @spillai

[devin-ai-integration]

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