docs: condense comments across the repo

Comments had drifted into multi-paragraph narrative (git commit
lineage, debugging stories, restated code) in several hot spots
(scripts/deploy, hermes-agent.nix, flake.nix, gitea.nix, headscale.nix).
Trim every comment to its load-bearing "why" — gotchas, safety
warnings, and non-obvious rationale survive verbatim in substance,
just tightened to 1-2 sentences; historical narrative and anything
already covered in CLAUDE.md is cut. No code/logic changed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UJqEmY1y3AYX3JoX4Y6b21

scripts/edit_secrets

@@ -36,10 +36,9 @@ if [ "$show" -eq 1 ]; then
   exec nix shell nixpkgs#sops -c sops --decrypt "$file"
 fi
 
-# sops opens $EDITOR on a temp file and re-encrypts only if it changed.
-# Pitfalls that cause "File has not changed, exiting":
-#   - $EDITOR unset: no editor is on the `nix shell` PATH -> bundle one.
-#   - GUI editor (code/zed) forks and returns instantly -> force --wait.
+# sops re-encrypts only if the $EDITOR session actually changed the temp file.
+# GUI editors (code/zed) return instantly unless forced to --wait, and if
+# $EDITOR is unset no editor exists on the `nix shell` PATH, so bundle one.
 editor="${VISUAL:-${EDITOR:-}}"
 extra=()
 case "$editor" in