docs(skills): document URL install across features, reference, guide, and hermes-agent skill (#16355)

Follow-up to #16323 — the UrlSource adapter is shipped but four
user-facing docs surfaces still only listed the hub-identifier forms.

- user-guide/features/skills.md: add ``url`` to the Supported-hub-sources
  table; add a new "#### 8. Direct URL (`url`)" section explaining scope
  (single-file SKILL.md only), name-resolution order (frontmatter → URL
  slug → interactive prompt → --name flag), and both TTY and
  non-interactive usage. Add two URL examples to the install-examples
  block near the top of the page.
- reference/cli-commands.md: two URL install examples + one note
  explaining the name-resolution fallback chain.
- guides/work-with-skills.md: one URL-install example alongside the
  existing hub-identifier examples.
- skills/autonomous-ai-agents/hermes-agent/SKILL.md: Quick Reference
  block's ``hermes skills install`` line now spells out that ID can be
  a hub identifier OR a direct SKILL.md URL, and mentions --name for
  frontmatter-less skills.

No code changes. No new dependencies. Website builds via the usual
Docusaurus pipeline.

Co-authored-by: teknium1 <teknium@noreply.github.com>

skills/autonomous-ai-agents/hermes-agent/SKILL.md

@@ -115,7 +115,7 @@ hermes tools disable NAME   Disable a toolset
 
 hermes skills list          List installed skills
 hermes skills search QUERY  Search the skills hub
-hermes skills install ID    Install a skill
+hermes skills install ID    Install a skill (ID can be a hub identifier OR a direct https://…/SKILL.md URL; pass --name to override when frontmatter has no name)
 hermes skills inspect ID    Preview without installing
 hermes skills config        Enable/disable skills per platform
 hermes skills check         Check for updates