fix: improve shell detection, curl flags, and cleanup robustness

- Use ZSH_VERSION instead of ZSH_NAME for reliable zsh detection
- Document NVIM_* env vars as optional external overrides
- Add -fsSL flags to curl for mise bootstrap
- Consolidate duplicate shellcheck directives in install-fonts.sh
- Add explicit return 0 to cleanup script helper functions
- Add actionable remediation to uv-not-found error message

local/bin/dfm

@@ -168,7 +168,7 @@ section_install()
       msgr run "Installing tools via mise..."
       if ! command -v mise &> /dev/null; then
         msgr nested "Installing mise..."
-        if ! curl https://mise.run | sh; then
+        if ! curl -fsSL https://mise.run | sh; then
           msgr err "Failed to install mise"
           exit 1
         fi