Add OrbitOS skills (bundled)

- orbites-research: deep research workflow
- orbites-parse-knowledge: structure unstructured text
- orbites-obsidian-markdown: Obsidian markdown reference
- obsidian: vault read/write/search
- Updated README: 20 skills total, OrbitOS bundled

skills/orbitos/orbites-obsidian-markdown/SKILL.md

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+---
+name: orbites-obsidian-markdown
+description: Obsidian Flavored Markdown reference — wikilinks, callouts, embeds, frontmatter, mermaid. Use when working with Obsidian vault files or user asks about wikilinks/callouts/embeds.
+---
+# OrbitOS: Obsidian Markdown Reference
+
+Obsidian uses CommonMark + GitHub Flavored Markdown + Obsidian extensions (wikilinks, callouts, embeds).
+
+## Internal Links (Wikilinks)
+
+```markdown
+[[Note Name]]
+[[Note Name|Display Text]]
+[[Note Name#Heading]]
+[[Note Name#^block-id]]
+![[Note Name]]                    # Embed entire note
+![[Note Name#Section]]             # Embed section
+```
+
+## Callouts
+
+```markdown
+> [!note] / [!info] / [!tip] / [!warning] / [!danger]
+> [!faq]- Collapsed by default
+> [!faq]+ Expanded by default
+```
+
+## Properties (Frontmatter)
+
+```yaml
+---
+title: My Note
+date: 2024-01-15
+tags: [project, important]
+aliases: [My Note, Alt Name]
+status: in-progress
+due: 2024-02-01T14:30:00
+---
+```
+
+## Embeds
+
+```markdown
+![[image.png|300]]         # Image with width
+![[audio.mp3]]              # Audio
+![[document.pdf#page=3]]    # PDF
+```
+
+## Other
+
+- **Highlight**: `==text==`
+- **Comments**: `%%hidden text%%`
+- **Math**: `$e^{i\pi} + 1 = 0$`
+- **Mermaid**: ```` ```mermaid ```` ````
+
+## Critical DO NOT
+
+- **No empty line after frontmatter** `---` (becomes visible in body)
+- Frontmatter MUST be at line 1
+- **NO duplicate keys** in frontmatter
+- Use array syntax for tags: `tags: [tag1, tag2]`