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).

Dockerfile.base

@@ -57,6 +57,12 @@ ENV DEBIAN_FRONTEND=noninteractive
 #                  pi-studio's container-loopback server to the container's
 #                  external interface so a published port can reach it.
 #                  ~1 MB; generally useful for any port-forwarding need.
+#   nano         — small, non-modal terminal editor for users who don't want
+#                  a vi-based editor. ~2.8 MB installed; its deps (libc6,
+#                  libncursesw6, libtinfo6) are already pulled in by nvim/less/
+#                  htop/tmux, so it adds no extra packages. Companion to nvim
+#                  and the `micro` binary installed further down. EDITOR stays
+#                  nvim; users opt in via `export EDITOR=nano`.
 RUN apt-get update && \
     apt-get upgrade -y --no-install-recommends && \
     apt-get install -y --no-install-recommends \
@@ -92,6 +98,7 @@ RUN apt-get update && \
     graphviz \
     imagemagick \
     socat \
+    nano \
     && ln -s /usr/bin/fdfind /usr/local/bin/fd \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*
@@ -231,6 +238,33 @@ RUN ARCH=$(case "${TARGETARCH}" in amd64) echo "x86_64" ;; arm64) echo "arm64" ;
     ln -s /opt/nvim-linux-${ARCH}/bin/nvim /usr/local/bin/nvim && \
     nvim --version | head -1
 
+# micro — modern, non-modal terminal editor. Ships alongside nvim so users
+# who aren't comfortable with vi-style modal editing have a friendly option:
+# desktop-style keybindings (Ctrl+S save, Ctrl+Q quit, Ctrl+C/V/X, Ctrl+Z
+# undo), mouse support, and syntax highlighting out of the box. A single
+# static Go binary (~12 MB) installed from GitHub releases, exactly like
+# bat/eza/zoxide below. EDITOR stays nvim (see below); users opt in with
+# `export EDITOR=micro` or `git config --global core.editor micro`.
+#
+# NOTE: upstream moved zyedidia/micro -> micro-editor/micro. The old org URL
+# still 302s, but its /releases/latest redirect lands on ANOTHER /latest URL
+# (the org rename), so the tag-parsing idiom below would resolve "latest"
+# instead of a version. Use the canonical micro-editor/micro URL.
+# Arch asset naming differs from the others: amd64 -> linux64, arm64 ->
+# linux-arm64. The tarball extracts to micro-<version>/micro.
+ARG MICRO_VERSION=latest
+RUN ARCH=$(case "${TARGETARCH}" in amd64) echo "linux64" ;; arm64) echo "linux-arm64" ;; *) echo "linux64" ;; esac) && \
+    V="${MICRO_VERSION}" && \
+    if [ "$V" = "latest" ]; then \
+      V=$(curl -sI --retry 5 --retry-delay 5 --retry-all-errors "https://github.com/micro-editor/micro/releases/latest" | awk 'tolower($1)=="location:" { sub(/\r$/,"",$2); n=split($2,a,"/"); print a[n] }'); \
+    fi && \
+    V="${V#v}" && [ -n "$V" ] && \
+    echo "Installing micro ${V}" && \
+    curl -fsSL --retry 5 --retry-delay 5 --retry-all-errors "https://github.com/micro-editor/micro/releases/download/v${V}/micro-${V}-${ARCH}.tar.gz" | tar -xz -C /tmp && \
+    install /tmp/micro-${V}/micro /usr/local/bin/micro && \
+    rm -rf /tmp/micro-${V} && \
+    micro --version
+
 # bat
 ARG BAT_VERSION=latest
 RUN ARCH=$(case "${TARGETARCH}" in amd64) echo "x86_64" ;; arm64) echo "aarch64" ;; *) echo "x86_64" ;; esac) && \