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/slot-beauty-dark-icons.nix

@@ -21,15 +21,11 @@ stdenvNoCC.mkDerivation {
   # the theme's own Inherits= chain (breeze-dark, Adwaita, hicolor) for those.
   dontCheckForBrokenSymlinks = true;
 
-  # index.theme's Directories= lists panel/16@2, panel/22@2, panel/24@2 (with
-  # Scale=2), but the actual on-disk dirs are named 16@2x/22@2x/24@2x (the
-  # correct freedesktop-spec suffix) — an upstream index.theme typo. That
-  # mismatch makes `gtk-update-icon-cache` refuse to emit ANY cache at all
-  # (exits 1, "The generated cache was invalid"), so unlike the other vendored
-  # themes here, this one ships with no icon-theme.cache and relies on GTK's
-  # live directory-scan lookup instead — functionally fine, just not
-  # cache-accelerated. gtk3's default postFixup hook (dropIconThemeCache)
-  # would strip a cache anyway, so there's nothing to opt out of.
+  # index.theme's Directories= names panel/16@2 etc. (Scale=2) but the
+  # on-disk dirs are 16@2x etc. (the correct suffix) — an upstream typo that
+  # makes `gtk-update-icon-cache` exit 1, so this theme ships uncached and
+  # relies on GTK's live directory scan instead (functionally fine, just not
+  # cache-accelerated).
   installPhase = ''
     runHook preInstall
     mkdir -p "$out/share/icons"