docs: update all docs for optional-skills and browse command

Update 7 documentation files to reflect:
- optional-skills/ directory in all project structure trees
- 'hermes skills browse' in all CLI command listings
- '/skills browse' in all slash command references
- Three-tier skill placement (bundled → optional → hub)
- 'official' trust level in trust level tables
- Updated /skills description from 'Search, install...' to 'Browse, search...'

Files updated:
- CONTRIBUTING.md (skill classification, project tree, section title)
- AGENTS.md (project tree, Skills Hub description, source adapters list)
- website/docs/reference/cli-commands.md (CLI table, slash command table)
- website/docs/developer-guide/creating-skills.md (structure, classification, trust)
- website/docs/user-guide/features/skills.md (hub commands, trust table, slash commands)
- website/docs/user-guide/cli.md (slash command description)
- website/docs/developer-guide/architecture.md (project tree)

website/docs/developer-guide/creating-skills.md

@@ -24,7 +24,7 @@ Make it a **Tool** when:
 
 ## Skill Directory Structure
 
-Bundled skills live in `skills/` organized by category:
+Bundled skills live in `skills/` organized by category. Official optional skills use the same structure in `optional-skills/`:
 
 ```
 skills/
@@ -98,14 +98,16 @@ Run the skill and verify the agent follows the instructions correctly:
 hermes chat --toolsets skills -q "Use the X skill to do Y"
 ```
 
-## Should the Skill Be Bundled?
+## Where Should the Skill Live?
 
 Bundled skills (in `skills/`) ship with every Hermes install. They should be **broadly useful to most users**:
 
 - Document handling, web research, common dev workflows, system administration
 - Used regularly by a wide range of people
 
-If your skill is specialized (a niche engineering tool, a specific SaaS integration, a game), it's better suited for a **Skills Hub** — upload it to a registry and share it via `hermes skills install`.
+If your skill is official and useful but not universally needed (e.g., a paid service integration, a heavyweight dependency), put it in **`optional-skills/`** — it ships with the repo, is discoverable via `hermes skills browse` (labeled "official"), and installs with builtin trust.
+
+If your skill is specialized, community-contributed, or niche, it's better suited for a **Skills Hub** — upload it to a registry and share it via `hermes skills install`.
 
 ## Publishing Skills
 
@@ -136,5 +138,6 @@ All hub-installed skills go through a security scanner that checks for:
 
 Trust levels:
 - `builtin` — ships with Hermes (always trusted)
+- `official` — from `optional-skills/` in the repo (builtin trust, no third-party warning)
 - `trusted` — from openai/skills, anthropics/skills
 - `community` — any findings = blocked unless `--force`