#1442 feat(obsidian): register wiki vault with cross-platform path

Summary

• Generate obsidian.json dynamically via Nix using config.home.homeDirectory so the vault path resolves correctly on both kyber (/home/ubuntu) and galactica (/Users/shunkakinoki)
• Set open = true on the vault so the headless daemon auto-opens it on startup, enabling the Obsidian CLI
• Enable the config on both isKyber and isGalactica (was kyber-only)

Test plan

• Verified obsidian help works on kyber after make switch + service restart
• Verify on galactica after next make switch

---

Summary by cubic

Registers the Obsidian wiki vault with a cross‑platform path and auto‑opens it on startup to enable the headless obsidian CLI. Fixes “Vault not found” on kyber and galactica.

• New Features
  • Dynamically generates obsidian.json via Nix using config.home.homeDirectory so the vault path resolves on both hosts.
  • Enables the config on kyber and galactica; sets open = true so the daemon opens the vault automatically.