Trim comments across Rust and webapp source to direct one-liners (ticket 030)

Pass over src/*.rs, webapp/src/**, and the in-app "?" docs prose:
condensed multi-paragraph doc comments to single lines that state the
non-obvious why, deleted comments that only restated adjacent code, and
tightened the Docs.tsx help-panel wording. No logic, structure, or code
formatting changed — verified via cargo test (143 passed) and
tsc -b && vite build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

src/timestamp.rs

@@ -1,11 +1,7 @@
 use serde::Serialize;
 use std::time::{SystemTime, UNIX_EPOCH};
 
-/// Wall-clock instant stored as nanoseconds since the Unix epoch.
-///
-/// The README's data model sketches this field as `Instant`, but `Instant` has no
-/// epoch and can't be serialized to the frontend, so wall-clock time is stored here
-/// instead.
+/// Wall-clock instant stored as nanoseconds since the Unix epoch (not `std::time::Instant`, which has no epoch and can't be serialized).
 #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Serialize)]
 pub struct Timestamp(i64);