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/methods.rs

@@ -123,7 +123,7 @@ define_methods! {
     ToolServerGetStatus => "tool_server.get_status",
     ToolServerEvict => "tool_server.evict",
 
-    // ── Session lifecycle ───────────────────────────────────────────
+    // Session lifecycle
 
     /// Full tool snapshot for a session (server → hub). Idempotent:
     /// re-sending replaces the tool set; the hub diffs and emits