Auto-cleanup dead systemlink & FS Cache Reflowing, Bump OTA Version to 1.0.76

feat/fix: Rich token usage popovers, robust LiteLLM context window bounds logic, and Skill management refactor

Refactor AI Config and Fix Login failure: Migrated services to a structured api directory, updated backend schemas for multiple TTS/STT providers, and improved settings/chat UI coverage.

feat: enhance node access control, user preferences, and skill management ...

- Secured node-related endpoints with group-based access control.
- Fixed user preference merging to preserve node attachments.
- Restricted modification and deletion of system skills.
- Hidden administrative node controls for non-admin users.
- Fixed WebSocket connectivity and permission checks for node mesh.
- Filtered node visibility in profile and swarm control to granted nodes only.

chore: backup local changes before investigation

fix(mesh/skills): fix incorrect get_db import causing uvicorn crash in production

feat(skills): central UI for creating, viewing, sharing and cloning LLM skills and workflows