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-tracing-macros/src/timed.rs

@@ -35,8 +35,6 @@ macro_rules! timed {
         value
     }};
 
-    // Logging-only variant with explicit log level:
-    // `timed!(log: info, "something", { ... })`
     (log: $lvl:ident, $name:expr, $block:block) => {{
         let start = ::std::time::Instant::now();
         let value = $block;
@@ -45,7 +43,9 @@ macro_rules! timed {
         value
     }};
 
-    // Sync Result variant (no `.await` inside the block)
+    // The `try:` arms wrap the block in an immediately-invoked closure (or
+    // async block) so a `?` inside it returns into the macro, which can then
+    // log the error and elapsed time, rather than escaping the caller.
     (try: $name:expr, $block:block) => {{
         let start = ::std::time::Instant::now();
         let result = (|| $block)();
@@ -62,8 +62,6 @@ macro_rules! timed {
         }
     }};
 
-    // Sync Result variant with explicit log level:
-    // `timed!(try: info, "something", { ... })?`
     (try: $lvl:ident, $name:expr, $block:block) => {{
         let start = ::std::time::Instant::now();
         let result = (|| $block)();
@@ -80,7 +78,6 @@ macro_rules! timed {
         }
     }};
 
-    // Async Result variant, for blocks that use `.await` / `?`.
     (try: $name:expr, async $block:block) => {{
         let start = ::std::time::Instant::now();
         let result = (async $block).await;
@@ -97,8 +94,6 @@ macro_rules! timed {
         }
     }};
 
-    // Async Result variant with explicit log level:
-    // `timed!(try: info, "something", async { ... })?`
     (try: $lvl:ident, $name:expr, async $block:block) => {{
         let start = ::std::time::Instant::now();
         let result = (async $block).await;

crates/codegen/kigi-tracing-macros/src/timestamp.rs

@@ -1,7 +1,7 @@
 //! Macros for printing messages with Unix timestamps.
 //!
-//! These macros use tracing for output, which is safe to use in headless mode
-//! (no terminal attached). The timestamp is included in the message.
+//! Output goes through tracing rather than stdout/stderr so these are safe in
+//! headless mode (no terminal attached).
 
 /// Prints a message via tracing::info with a Unix timestamp prefix.
 ///