feat(banner): show what is new in 3.2, readable at 80 columns

[LESdylan]

The welcome panel's "Did you know?" block becomes What's new in 3.2: one row per new feature, written as the keys that reach it, then the switch for inline hints. The panel links to a new guide, wiki/whats-new.md, at univers42.github.io/hellish/whats-new. The guide covers every feature with an example run on a 3.2 build.

│           Welcome back, friend!           │ Getting started                  │
│                                           │                                  │
│                 :::      ::::::::         │   help       commands & options  │
│               :+:      :+:    :+:         │   update     check for updates   │
│             +:+ +:+         +:+           │   type NAME  what a name runs    │
│           +#+  +:+       +#+              │ ──────────────────────────────── │
│         +#+#+#+#+#+   +#+                 │  NEW  What's new in 3.2          │
│              #+#    #+#                   │                                  │
│             ###   ########.fr             │   ↑ ↓        history by prefix   │
│                                           │   make <TAB> Makefile targets    │
│  hellish 3.1.3 · a POSIX shell with bite  │   bind -x    key runs a command  │
│                     ~                     │   bindkey    zsh binds now work  │
│                                           │   ${var@P}   render as a prompt  │
│       the 3.2 guide, with examples        │   $SRANDOM   and $EPOCHREALTIME  │
│  → univers42.github.io/hellish/whats-new  │                                  │
│                                           │   export HELLISH_AUTOSUGGEST=1   │
│                                           │   → ^F End   take the dim hint   │
│                                           │   Alt-F      take one word       │
│                                           │   Alt-N/P    older/newer hint    │

(80 columns, rendered from this branch)

• Fits 80 columns. The right column has 32 cells there. The 3.1 rows, and two "Getting started" rows, were written for about 40 and were cut with …. The link sits under the logo, because the left column is a fixed 43 columns.
• LANG=C frame. The identity line printed a UTF-8 · that header_width() cannot decode in that locale, so the row came out too wide. It is a - there now.
• HELLISH_HEADER_REV goes to 4. banner_update_test.py now reads the revision from incs/version.h instead of hard-coding it as 3.
• The guide is in the mkdocs nav. mkdocs build --strict passes, and every in-page anchor resolves. interactive.md's autosuggestions roadmap entry is now marked shipped.

Tests: tests/banner_news_test.py (new, 27 checks) renders the panel at 80 and 120 columns in UTF-8 and C. It checks four things:

• every framed row is exactly the terminal's width;
• no news row is clipped;
• the link shows in full;
• the guide is in the nav and names every key the banner shows, so the two cannot drift apart.

It fails 7 checks on the 3.1.3 build. Lengthening one row makes it fail at 80 columns only. banner_update_test.py passes all 16 checks with a clean HOME. A personal ~/.hellishrc prompt hides the update badge, both before and after this change.

🤖 Generated with Claude Code