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-shared/src/session/info.rs

@@ -1,6 +1,5 @@
 use agent_client_protocol as acp;
 
-/// Session identity: `id` + `cwd`.
 #[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
 pub struct Info {
     pub id: acp::SessionId,

crates/codegen/kigi-shared/src/session/mod.rs

@@ -13,15 +13,12 @@ pub use info::Info;
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct FeedbackTerminalInfo {
-    /// Terminal emulator brand (e.g. "Ghostty", "iTerm2", "Unknown").
+    /// e.g. "Ghostty", "iTerm2", "Unknown".
     pub brand: String,
-    /// Multiplexer wrapping the session (e.g. "tmux", "Zellij", "None detected").
+    /// e.g. "tmux", "Zellij", "None detected".
     pub multiplexer: String,
-    /// Whether the session is over SSH.
     pub is_ssh: bool,
-    /// Whether Byobu is wrapping the session.
     pub is_byobu: bool,
-    /// Raw `TERM` environment variable value.
     pub term_var: String,
     /// tmux server version if inside tmux, otherwise "n/a".
     #[serde(default, skip_serializing_if = "Option::is_none")]