docs(comments): rewrite comments across all crates to the guidelines

Sweep every first-party crate source (1956 .rs files) to the project comment
guidelines: delete redundant restatements, decorative banners, change
narration, and end-of-line comments; keep and tighten the crucial ones
(invariants, bug rationale, SAFETY blocks, ported-source attribution).

No functional code changed. Every edit is proven comment-only against the
prior tree by a comment-stripping lexer (string/char/raw-string aware) plus a
separate doctest-fence check. Where removing a comment made rustfmt or clippy
want to re-lay-out adjacent code, the minimal triggering comment is restored so
code tokens stay byte-identical.

Gates green: cargo fmt --all --check (0 diffs), cargo check and cargo clippy
--workspace --all-targets (0 warnings).

Adds scripts/check_codegen_comment_guidelines.py — the enforcement gate for
these guidelines (flags banners, end-of-line comments, change narration, and
commented-out code).

crates/codegen/kigi-tui/src/plugin_cmd.rs

@@ -18,8 +18,6 @@ use kigi_agent::plugins::install_registry::{InstallKind, InstallRegistry};
 use kigi_agent::plugins::manifest::{ManifestLoadResult, PluginManifest, load_manifest};
 use kigi_shell::plugin::{self, RepoUpdateOutcome, UninstallError};
 
-// ── JSON output types ───────────────────────────────────────────────
-
 /// Typed entry for `kigi plugin list --json`. The `status` field is a stable
 /// discriminator for machine consumers.
 #[derive(Serialize)]
@@ -34,8 +32,6 @@ enum PluginEntry {
     },
 }
 
-// ── CLI arg definitions ─────────────────────────────────────────────
-
 #[derive(Debug, clap::Args, Clone)]
 pub struct PluginArgs {
     #[command(subcommand)]
@@ -114,8 +110,6 @@ pub enum PluginCommand {
     },
 }
 
-// ── Helpers ─────────────────────────────────────────────────────────
-
 fn kind_label(kind: &InstallKind) -> String {
     match kind {
         InstallKind::Git { url, .. } => format!("git: {url}"),
@@ -156,8 +150,6 @@ fn trust_prompt(subject: &str, source_arg: &str) -> String {
     )
 }
 
-// ── Top-level dispatch ──────────────────────────────────────────────
-
 pub async fn run(args: PluginArgs) -> Result<()> {
     match args.command {
         PluginCommand::List { json } => cmd_list(json),
@@ -181,8 +173,6 @@ pub async fn run(args: PluginArgs) -> Result<()> {
     }
 }
 
-// ── Plugin subcommands ──────────────────────────────────────────────
-
 fn cmd_list(json: bool) -> Result<()> {
     let registry = InstallRegistry::load();
     let repos = registry.list();