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/sdlc/assets/workflow.puml

@@ -0,0 +1,34 @@
+@startuml sdlc-workflow
+skinparam defaultFontName Arial
+skinparam backgroundColor #FAFAFA
+
+actor Developer
+participant "sdlc Skill" as SKILL
+participant "specs/" as FS
+
+Developer -> SKILL : describe project
+SKILL -> FS : write requirements.md
+SKILL --> Developer : phase 1 complete ✓
+Developer -> SKILL : "done"
+
+SKILL -> FS : write design.md
+SKILL --> Developer : phase 2 complete ✓
+Developer -> SKILL : "done"
+
+SKILL -> FS : write tasks.md
+SKILL --> Developer : phase 3 complete ✓
+Developer -> SKILL : "done"
+
+SKILL -> FS : write impl-plan.md
+SKILL --> Developer : phase 4 complete ✓
+Developer -> SKILL : "done"
+
+SKILL -> FS : write source code
+SKILL -> FS : run tests → update STATUS.md
+SKILL --> Developer : phase 5 & 6 complete ✓
+
+note over Developer, SKILL
+  At any point: "continue" resumes from STATUS.md
+  After completion: describe a CR to add features
+end note
+@enduml