feat: ship nano + micro (non-modal editors) alongside nvim

The image shipped only nvim (EDITOR=nvim), a modal vi-style editor. Add
both a classic and a modern non-modal option so users who aren't
comfortable with vi keybindings have a choice:

- nano (apt): ~2.8 MB installed; deps (libc6, libncursesw6, libtinfo6)
  already present via nvim/less/htop/tmux, so no extra packages pulled in.
- micro: ~12 MB single static Go binary from GitHub releases (same pattern
  as bat/eza/zoxide). Desktop-style keys (Ctrl+S/Ctrl+Q), mouse, syntax
  highlighting. ARG MICRO_VERSION pins; defaults to latest.

Combined ~15 MB (well within the smoke size threshold's ~250 MB headroom,
so no threshold bump). EDITOR stays nvim; both editors are opt-in
(export EDITOR=micro | nano). Uses the canonical micro-editor/micro URL
because the old zyedidia/micro org rename makes /releases/latest redirect
to another /latest, defeating the tag-parsing latest-resolution idiom
(independently verified: old org 302s to micro-editor/micro; both arch
tarballs HTTP 200; latest resolves to v2.0.15).

Base-image change, so it lands on the next base-<hash> rebuild. Updates
README (what's-inside tree + EDITOR note), CHANGELOG (Unreleased/Added),
and smoke-test.sh (nano + micro presence checks). Ported from pi-devbox
3a59e15.

README.md

@@ -263,6 +263,11 @@ volumes:
   - ~/.config/nvim:/home/developer/.config/nvim:ro
 ```
 
+> **Not a vi person?** The image also ships two non-modal editors alongside nvim:
+> **nano** (classic, minimal) and **micro** (modern — desktop-style `Ctrl+S`/`Ctrl+Q`
+> keys, mouse, syntax highlighting). `EDITOR` stays `nvim`; opt in per-shell with
+> `export EDITOR=nano` (or `micro`), or for git with `git config --global core.editor micro`.
+
 ### Python development with uv
 
 The image includes Python 3.13 (from Debian Trixie) and [uv](https://docs.astral.sh/uv/), a fast Python package manager that replaces pip, venv, and pyenv:
@@ -807,7 +812,7 @@ Container (Debian trixie)
 ├── opencode binary
 ├── oh-my-opencode-slim (optional — multi-agent orchestration plugin, includes Bun)
 ├── AWS CLI v2 (SSO + Bedrock auth)
-├── neovim 0.12, tmux, htop, bat, eza, zoxide, uv, rustup, make, gcc, g++, rsync
+├── neovim 0.12, nano, micro, tmux, htop, bat, eza, zoxide, uv, rustup, make, gcc, g++, rsync
 ├── git, git-crypt, age, gitleaks, ssh, ripgrep, fd, fzf, jq, curl, tree
 ├── Node.js (for MCP servers)
 ├── Bun (optional — included with oh-my-opencode-slim)