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/lib.rs

@@ -23,7 +23,6 @@ pub mod mcp_cmd;
 pub mod memory_cmd;
 pub mod memory_release;
 pub mod memory_trace;
-// ── Minimal (scrollback-native) mode seam ────────────────────────────────────
 // The *only* minimal-specific surface in this (the "full pager") crate. Both
 // modules are grouped under `src/minimal/` so a full-pager contributor sees one
 // folder to ignore, not files scattered through the module list. All the actual