feat: retool setup scripts as Debian 13-first (keep Fedora support)

- main-setup.sh: sudo/root preflight for fresh Debian installs; offer
  distro-agnostic 03-dotnet-setup.sh on all supported distros
- 01-package-install.sh: Debian package renames (bind9-dnsutils), batcat
  symlink, libvirt/QEMU stack; vendor repos for gh/terraform/kubectl +
  k9s/minikube binaries (not in Debian main); keep dnf path for Fedora
- 02-dev-tools-setup.sh: PEP 668 fallback for pynvim pip install
- 03-fedora-dotnet-setup.sh -> 03-dotnet-setup.sh: .NET SDK via official
  dotnet-install.sh (no MS repo), PostgreSQL + Podman/podman-docker
- zshrc: purge dead oh-my-zsh references (prompt is Oh-My-Posh)
- README: Debian 13 first-class; docs: record decisions + status

docs/debian-13-migration-plan.md

@@ -4,6 +4,15 @@ Goal: make this dotfiles repo fully suited for **Debian 13 (trixie)** so a fresh
 
 Working branch: `debian-13` (base: `master`).
 
+> **Status: implemented on this branch** (see `git log` on `debian-13`). Recorded decisions below.
+
+### Decisions (user-confirmed)
+1. **Container runtime:** Podman (`podman`, `podman-compose`, `podman-docker` shim) — no Docker CE / moby-engine.
+2. **VS Code:** keep the **Flatpak** install (`com.visualstudio.code`); no MS apt/rpm repo for the editor.
+3. **.NET install:** official **`dotnet-install.sh`** (channel `STS`, overridable via `DOTNET_CHANNEL`) — no Microsoft vendor repo.
+4. **oh-my-zsh:** **purge** its remnants from `zshrc` (now plain zsh + Oh-My-Posh).
+5. **Scope:** **full rework** applied to `main-setup.sh` and all `scripts/*.sh`, `zshrc`, `README.md`.
+
 ---
 
 ## 1. Summary of what changes