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-shell/src/inspect/mod.rs

@@ -338,7 +338,6 @@ async fn build_report(cwd: &Path) -> InspectReport {
         list_skills(cwd, &plugin_registry, &skills_config),
     );
 
-    // Attach local compatibility status to each discovered vendor entry.
     for entry in &mut instructions {
         entry.compatibility_status =
             instruction_compat_status(&entry.vendor, &entry.file_type, &external_compat);
@@ -651,7 +650,6 @@ fn list_hooks(
         })
         .collect();
 
-    // Plugin hooks
     for p in discovered_plugins {
         if !p.trusted {
             continue;
@@ -973,7 +971,6 @@ fn list_config_sources(cwd: &Path) -> ConfigSources {
         }
     }
 
-    // User managed
     if let Some(home) = crate::config::user_kigi_home() {
         let p = home.join("managed_config.toml");
         if let Some((path_s, note)) = describe_config_file(&p) {
@@ -1716,8 +1713,6 @@ mod tests {
         );
     }
 
-    // ── skill source mapping (skill_entry_source) ─────────────────────────
-
     fn skill_fixture(name: &str, path: &str, scope: SkillScope) -> SkillInfo {
         SkillInfo {
             name: name.to_string(),