style: align comments with the project conventions

Apply a codebase-wide comment audit against the comment conventions:
split banned semicolons and multi-sentence lines into one sentence per
line, cut cross-file and history narration, trim file-top headers to a
single purpose line, and drop verbosity that did not earn its place.
Prose docs (CLAUDE.md, install.md) get the same one-sentence-per-line
and no-semicolon treatment.

modules/agents/skills.nix

@@ -1,13 +1,6 @@
 { config, inputs, ... }:
-# Global agent skills from the skills flake, placed under the agent harness's
-# skills directory so they are active in every project. The flake's home-manager
-# module self-gates on the harness being enabled and installs nothing for an
-# empty selection, so a host without one carries no skills either way.
-#
-# Unlike every other module, this one declares no `enable` flag and wires
-# unconditionally, by design.
-# The flake's self-gating above already makes it inert where the harness is
-# absent, so a gate would guard nothing.
+# Global agent skills, placed under the skills directory so they are active in
+# every project.
 let
   user = config.user.name;