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

pkgs/azure-glassy-dark-icons.nix

@@ -17,13 +17,11 @@ stdenvNoCC.mkDerivation {
 
   dontBuild = true;
 
-  # Upstream ships a handful of dangling symlinks under mimetypes/16 (e.g.
-  # libreoffice-spreadsheet.svg -> libreoffice-oasis-spreadsheet.svg, which
-  # doesn't exist in that size dir) — a minor packaging bug in the theme
-  # itself. Harmless: GTK's icon lookup just falls through to the theme's
-  # own Inherits= chain (breeze-dark, breeze, Adwaita, hicolor) for those few
-  # mimetypes. Nixpkgs' default noBrokenSymlinks fixup check would otherwise
-  # fail the whole build over it.
+  # Upstream ships a handful of dangling symlinks under mimetypes/16 (e.g. a
+  # target that doesn't exist in that size dir) — harmless, GTK's own
+  # Inherits= chain (breeze-dark, breeze, Adwaita, hicolor) covers the
+  # fallback. Nixpkgs' default noBrokenSymlinks check would otherwise fail
+  # the build over it.
   dontCheckForBrokenSymlinks = true;
 
   # gtk3's setup hook strips icon-theme.cache from $out by default