SKILL.md: add v0.2.2 features (--no-subscribe, --subscribe, config trust, new global flags)

[aaajiao]

The SKILL.md doesn't document several features added in v0.2.2 (#187, #181):

Subscription control on create commands

--no-subscribe and --subscribe are available on messages create, docs documents create, and schedule create, but the SKILL.md doesn't mention them.

Suggested additions:

• Messages section: add --no-subscribe / --subscribe "people" flags and examples
• Files & Documents section: add --no-subscribe example for docs documents create
• Schedule section: add --no-subscribe example for schedule create
• Quick Reference table: add a "Post silently" row

Config trust model

basecamp config trust / basecamp config untrust (#181) are not documented in the Configuration section.

New global flags

--styled, -v / -vv (verbose), and --md (markdown output) are missing from the Output Modes section.

These are especially important for AI agent use cases — --no-subscribe is the clean way to do silent/automated posting without manual subscription management after creation.