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-agent/src/plugins/manifest.rs

@@ -154,7 +154,7 @@ pub struct PluginManifest {
     #[serde(default)]
     pub keywords: Vec<String>,
 
-    // ── Component path overrides (supplement convention dirs) ──────
+    // Component path overrides (supplement convention dirs)
     #[serde(default)]
     pub skills: Option<PathOrPaths>,
     #[serde(default)]
@@ -247,7 +247,7 @@ impl PluginManifest {
 
     /// Log informational messages about manifest features.
     ///
-    /// Called during discovery. Inline hooks and MCP servers are now
+    /// Called during discovery. Inline hooks and MCP servers are
     /// fully supported; this method logs when they are detected.
     pub fn warn_unsupported_features(&self, plugin_name: &str) {
         if self.inline_hooks().is_some() {
@@ -287,7 +287,7 @@ fn resolve_dirs(
     }
 }
 
-// ── Manifest loading ──────────────────────────────────────────────────
+// Manifest loading
 
 /// Manifest search order within a plugin directory.
 const MANIFEST_PATHS: &[&str] = &[
@@ -375,7 +375,7 @@ pub fn normalize_inline_mcp_servers(value: &serde_json::Value) -> serde_json::Va
     serde_json::json!({ "mcpServers": inner })
 }
 
-// ── Errors ────────────────────────────────────────────────────────────
+// Errors
 
 #[derive(Debug, thiserror::Error)]
 pub enum ManifestError {
@@ -530,7 +530,8 @@ mod tests {
         );
         assert_eq!(
             name_from_dirname(Path::new("/path/to/---")),
-            None // all hyphens after trim
+            // all hyphens after trim
+            None
         );
     }