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

The image shipped only nvim (EDITOR=nvim), a modal vi-style editor. Not
everyone is comfortable with vi keybindings, so add both a classic and a
modern non-modal option:

- 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 (<0.5% of the ~3.2 GB image). EDITOR stays nvim; both new
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.

Base-image change, so it lands on the next base-<hash> rebuild. Updates
README tool table + EDITOR note, CHANGELOG (Unreleased/Added), and
smoke-test.sh (nano + micro presence checks).

scripts/smoke-test.sh

@@ -6,6 +6,7 @@
 # Verifies:
 #   - pi binary present and (if EXPECTED_PI_VERSION set) matches CI's resolved version
 #   - new v1.0.0 base additions (pandoc, graphviz, imagemagick, yq, tealdeer)
+#   - non-modal editors nano + micro (alongside nvim)
 #   - tmux 0-indexing baked in /etc/tmux.conf (required for pi-studio variants)
 #   - pi-toolkit cloned at /opt/pi-toolkit
 #   - pi-extensions cloned at /opt/pi-extensions
@@ -24,7 +25,8 @@ set -euo pipefail
 IMAGE="${1:?usage: $0 <image>}"
 PASS=0; FAIL=0
 # pi-devbox v1.0.0 (decoupled from opencode-devbox) added pandoc, graphviz,
-# imagemagick, yq, tealdeer, and a baked /etc/tmux.conf. Local arm64 build
+# imagemagick, yq, tealdeer, a baked /etc/tmux.conf, and the non-modal
+# editors nano + micro (~15 MB combined). Local arm64 build
 # observed 3.20 GB. CI amd64 builds may differ slightly; threshold below
 # carries +300 MB margin to absorb arch differences without false reds.
 # Tighten in a follow-up release once amd64 actuals are observed in CI logs.
@@ -71,6 +73,8 @@ run "git"             "git --version"
 run "aws"             "aws --version"
 run "uv"              "uv --version"
 run "nvim"            "nvim --version"
+run "nano"            "nano --version"
+run "micro"           "micro --version"
 run "mempalace-mcp"   "mempalace-mcp --help"
 # v1.0.0 base additions — verify presence and basic functionality.
 run "pandoc"          "pandoc --version"