Add Skills and Plugins documentation (OpenHands#339)

* Add comprehensive skills and plugins documentation

- Update keyword.mdx example to use github skill instead of yummy example
- Add context management note explaining github/gitlab skills triggering
- Create Adding New Skills guide explaining /add-skill action and storage locations
- Create Creating New Skills guide with best practices for scope, naming, triggers, and content
- Create Plugins overview explaining plugin structure and comparison with skills
- Update docs.json navigation to include new pages in appropriate sections
- Add cross-references between related documentation pages for better user flow

Co-authored-by: openhands <openhands@all-hands.dev>

* Add reference to skill-creator skill in Creating New Skills guide

- Add Tip callout in Quick Start section mentioning skill-creator
- Explain that users can ask OpenHands to 'create a skill' for guided assistance
- Helpful for new users learning best practices

Co-authored-by: openhands <openhands@all-hands.dev>

* Reorder Quick Start to emphasize skill-creator as easiest approach

- Move skill-creator to be the first and primary method
- Present manual approach as alternative for those who prefer it
- Make it clear that skill-creator is the recommended starting point
- Better reflects that guided creation is simpler than manual setup

Co-authored-by: openhands <openhands@all-hands.dev>

* Fix JSON syntax errors in docs.json

- Add missing comma after overview/plugins on line 48
- Add missing comma after overview/skills/creating on line 59
- Resolves Mintlify broken links check failure

Co-authored-by: openhands <openhands@all-hands.dev>

* Address PR OpenHands#339 review feedback: Add monitoring docs and remove superlatives

- Create dedicated monitoring.mdx page (169 lines) for production skill monitoring
  - 4-part workflow: logging, evaluating, dashboarding, aggregating
  - Practical PR review examples with actual metrics
  - Links to SDK observability guide and GitHub workflows

- Update creating.mdx: Remove superlatives, add monitoring links
  - 'Easiest' → 'Automated Approach'
  - Added Info callout linking to monitoring page
  - Enhanced Further Reading with monitoring + observability links

- Update plugins.mdx: Remove conversational tone
  - 'Think of' → direct statement
  - 'knowledge packages' → 'specialized prompts'
  - 'Easy' → 'Quick'

- Update skills.mdx: Add monitoring link to Learn More section

- Add DOCS_UPDATES.md: Complete change log with justifications

All changes maintain technical, down-to-earth tone without superlatives.

Co-authored-by: openhands <openhands@all-hands.dev>

* Delete DOCS_UPDATES.md

* Update adding.mdx

* Update overview/plugins.mdx

Co-authored-by: OpenHands Bot <contact@all-hands.dev>

* Update docs.json

Co-authored-by: OpenHands Bot <contact@all-hands.dev>

* Remove duplicate navigation entries in docs.json

- Remove 'prompting-best-practices' from Onboarding (already in Essential Guidelines)
- Remove 'overview/skills/repo' from Onboarding (already in Skills group under Essential Guidelines)
- Remove 'model-context-protocol' from Product Guides (already in Essential Guidelines)
- Remove Skills group from Product Guides (already in Essential Guidelines)

Co-authored-by: openhands <openhands@all-hands.dev>

* docs: move creating/monitoring skills into Skills group for better discoverability

This change consolidates all skills-related documentation under the Skills
group for better discoverability, addressing reviewer feedback about
navigation organization clarity.

All skills pages are now grouped together:
- overview/skills (overview)
- overview/skills/repo
- overview/skills/keyword
- overview/skills/org
- overview/skills/public
- overview/skills/adding
- overview/skills/creating
- overview/skills/monitoring

* Clarify GITHUB_TOKEN usage for private skills

Address review comment: clarify that GITHUB_TOKEN is automatically used
by /add-skill command via GitHub API, and distinguish from manual git clone
authentication methods like SSH keys or token in URL.

* Address remaining review comments

- Fix hook command template syntax: use $OPENHANDS_PROJECT_DIR instead
  of unsupported {file_path} syntax, document available env vars
- Complete SDK example: add LLM, Agent imports and SecretStr usage
- Add skill-creator context: link to public skills library

---------

Co-authored-by: openhands <openhands@all-hands.dev>
Co-authored-by: OpenHands Bot <contact@all-hands.dev>

Author: 3 people

docs.json

@@ -43,8 +43,7 @@
             "group": "Onboarding OpenHands",
             "pages": [
               "openhands/usage/customization/repository",
-              "openhands/usage/customization/hooks",
-              "overview/skills/repo"
+              "openhands/usage/customization/hooks"
             ]
           },
           {
@@ -59,9 +58,13 @@
                   "overview/skills/repo",
                   "overview/skills/keyword",
                   "overview/skills/org",
-                  "overview/skills/public"
+                  "overview/skills/public",
+                  "overview/skills/adding",
+                  "overview/skills/creating",
+                  "overview/skills/monitoring"
                 ]
               },
+              "overview/plugins",
               {
                 "group": "Automations",
                 "pages": [