chore: restructure skills repo with new agents and skill bundles

- Add new skills: deep-dive, docs-rag, meta-creator, ppt-maker, sdlc
- Add agent configs: g-assistent, meta-creator, sdlc with prompt files
- Add reference docs for custom agents and skills specification
- Add utility scripts: install-agents.sh, orchestrate.py, puml2svg.sh
- Update README and commit-message skill config
- Remove deprecated skills: codereview, python, testing, typescript
- Add .gitignore

skills/deep-dive/assets/workflow.puml

@@ -0,0 +1,23 @@
+@startuml deep-dive-workflow
+skinparam defaultFontName Arial
+skinparam backgroundColor #FAFAFA
+
+actor Developer
+participant "deep-dive\nSkill" as SKILL
+participant "Input Source" as SRC
+participant "report-template.md" as TMPL
+
+Developer -> SKILL : "deep dive into X"\n(files / URL / topic / text)
+SKILL -> SRC : read files / fetch URL / analyze text
+SRC --> SKILL : raw material
+
+SKILL -> TMPL : load 11-section template
+SKILL -> SKILL : analyze architecture,\ndata model, flows, APIs
+
+loop each relevant section
+  SKILL -> SKILL : generate PlantUML diagram\n(component / ER / sequence)
+  SKILL -> SKILL : fill section content
+end
+
+SKILL --> Developer : deep-dive-{subject}.md
+@enduml