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/unified_log.rs

@@ -120,22 +120,18 @@ pub async fn flush_blocking() {
     let _ = kigi_acp_lib::acp_send(notification, tx).await;
 }
 
-/// Log an info-level entry.
 pub fn info(msg: &str, sid: Option<&str>, ctx: Option<serde_json::Value>) {
     push_entry(LogLevel::Info, msg, sid, ctx);
 }
 
-/// Log a warn-level entry.
 pub fn warn(msg: &str, sid: Option<&str>, ctx: Option<serde_json::Value>) {
     push_entry(LogLevel::Warn, msg, sid, ctx);
 }
 
-/// Log an error-level entry.
 pub fn error(msg: &str, sid: Option<&str>, ctx: Option<serde_json::Value>) {
     push_entry(LogLevel::Error, msg, sid, ctx);
 }
 
-/// Log a debug-level entry.
 pub fn debug(msg: &str, sid: Option<&str>, ctx: Option<serde_json::Value>) {
     push_entry(LogLevel::Debug, msg, sid, ctx);
 }