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).

CHANGELOG.md

@@ -13,6 +13,33 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
 
 ## Unreleased
 
+### Added
+
+- **Two non-modal terminal editors alongside `nvim`: `nano` and `micro`.**
+  The image previously shipped only `nvim` (with `EDITOR=nvim`), a modal
+  vi-style editor. Not everyone is comfortable with vi keybindings, so both
+  a classic and a modern non-modal option now ship:
+  - **`nano`** (apt) — ~2.8 MB installed. Its dependencies (`libc6`,
+    `libncursesw6`, `libtinfo6`) are already present via `nvim`/`less`/`htop`/
+    `tmux`, so it pulls in **no extra packages**. On-screen shortcut hints
+    (`^O` write, `^X` exit) make it the lowest-friction fallback.
+  - **`micro`** — ~12 MB, a single static Go binary installed from GitHub
+    releases (same pattern as `bat`/`eza`/`zoxide`). 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. Pin with
+    `--build-arg MICRO_VERSION=vX.Y.Z`; defaults to `latest`.
+
+  Combined footprint is ~15 MB (<0.5% of the ~3.2 GB image). **`EDITOR`
+  stays `nvim`** — the new editors are opt-in via `export EDITOR=micro`
+  (or `nano`) and/or `git config --global core.editor micro`.
+
+  Note: micro's upstream repo moved `zyedidia/micro` → `micro-editor/micro`;
+  the Dockerfile uses the canonical URL because the old org's
+  `/releases/latest` redirect lands on another `/latest` URL (the org
+  rename), which would defeat the tag-parsing `latest`-resolution idiom.
+  These are base-image additions, so they only land once the `base-<hash>`
+  rebuilds (this file changed, so the next build picks them up).
+
 ### Added (CI)
 
 - **Workflow lint (`.gitea/workflows/lint.yml`) running on every push and PR.**