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/common/kigi-tool-protocol/src/error_wire.rs

@@ -52,9 +52,7 @@ pub enum ToolErrorWire {
     #[error("behavior_version unsupported")]
     BehaviorVersionUnsupported { tool_id: ToolId, requested: String },
 
-    /// Render-card budget exceeded for the current session. `card_id`
-    /// carries the offending render-card identifier when known; `reason`
-    /// is a free-form human-readable explanation.
+    /// Render-card budget exceeded for the current session.
     #[error("render limited for {tool_id}: {reason}")]
     RenderLimited {
         tool_id: ToolId,
@@ -74,10 +72,9 @@ pub enum ToolErrorWire {
     Internal {
         #[serde(default, skip_serializing_if = "Option::is_none")]
         request_id: Option<RequestId>,
-        /// Bounded, human-readable cause of the internal error. Optional for
-        /// wire compatibility with older peers; producers SHOULD populate it
-        /// (truncated at the producer) so receivers can distinguish failure
-        /// modes without correlating server logs.
+        /// Optional for wire compatibility with older peers; producers SHOULD
+        /// populate it (truncated at the producer) so receivers can distinguish
+        /// failure modes without correlating server logs.
         #[serde(default, skip_serializing_if = "Option::is_none")]
         detail: Option<String>,
     },