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

webapp/src/lib/docsNav.tsx

@@ -1,6 +1,6 @@
 import { createContext, useCallback, useContext, useMemo, useRef, useState, type ReactNode } from 'react'
 
-/** One request to open the Docs panel scrolled to a specific section (ticket 021). */
+// One request to open the Docs panel scrolled to a specific section.
 export interface DocsTarget {
   sectionId: string
   /** Bumped on every request, even to the same section, so a repeat click re-triggers the flash. */