build(just): add 'bump' task for one-command version updates

Manually bumping a version requires touching 3+ files:
  * mix.exs (the canonical version)
  * github-page/index.html (the curl example)
  * README.md (the Publishing section's release flow + examples)

It's easy to forget one — this v0.2.0 -> v0.2.1 bump missed
github-page/index.html (caught in a follow-up commit).

Add a 'just bump <version>' recipe that:
  1. Reads the current version from mix.exs
  2. Validates the new version is a semver string and != current
  3. sed-updates all 3 files
  4. Prints reminders for files that need a human (CHANGELOG,
     AGENTS.md coverage stat, the skills' own version field)
  5. Prints the resulting diff for review

The task is local-only (the maintainer runs it on their laptop
before committing). It uses BSD sed -i '' syntax (macOS). On
Linux the maintainer would need to swap to 'sed -i' (no empty
arg) — left as-is since the task isn't run in CI.

Verified:
  * just bump 9.9.9  — works, leaves correct diff
  * just bump 0.2.1  — refuses (same as current)
  * just bump foo    — refuses (not a semver)
  * just bump        — refuses (no arg, just shows usage)

Author: gilbertwong96

justfile

@@ -148,3 +148,101 @@ check: ci test
 # Full build + test + release
 all: ci test release
     @echo "✅ All checks passed, release built"
+
+# ── Version Bumping ────────────────────────────────────────────────────
+# Bump the version across every source file that references it.
+# Usage: just bump 0.2.2
+#
+# Updates:
+#   * mix.exs                  — the canonical version
+#   * github-page/index.html   — the "Download binary" curl example
+#   * README.md                — the Publishing section's release flow
+#                                 (tag, push, npm-publish.sh, etc.)
+#
+# Reminds you (but does NOT auto-update):
+#   * CHANGELOG.md             — needs a human-written entry
+#   * AGENTS.md                — has a coverage stat quoted per-version
+#   * priv/skills/*            — the `version:` frontmatter is the SKILL's
+#                                 own version, not the binary's; leave
+#                                 alone unless you also bump the skills
+#
+# Files the bump task leaves alone (intentionally):
+#   * npm/*/package.json       — template files at the previous version;
+#                                 scripts/npm-publish.sh bumps at runtime
+#   * npm/@gilbertwong1996-ado-{platform}/bin/ado{,.exe} — downloaded
+#                                 from the GitHub Release by the publish
+#                                 script
+#   * lib/ado_cli/version.ex   — the AdoCli.Version module reads the
+#                                 version dynamically from mix.exs;
+#                                 there's no hard-coded string
+#
+# The task is idempotent: running it twice with the same arg is a
+# no-op (the second pass sees nothing to change).
+bump new_version:
+    #!/usr/bin/env bash
+    set -euo pipefail
+    NEW="{{new_version}}"
+
+    # Current version from mix.exs
+    OLD=$(grep -E '^\s*version:\s*"' mix.exs | head -1 | sed -E 's/.*"([^"]+)".*/\1/')
+    if [[ -z "$OLD" ]]; then
+        echo "ERROR: couldn't read current version from mix.exs" >&2
+        exit 1
+    fi
+    if [[ -z "$NEW" ]]; then
+        echo "Usage: just bump <new-version>  (e.g. just bump 0.2.2)" >&2
+        exit 1
+    fi
+    if [[ "$OLD" == "$NEW" ]]; then
+        echo "ERROR: new version ($NEW) is the same as current version ($OLD)" >&2
+        exit 1
+    fi
+    # Sanity-check the new version looks like a semver string. We
+    # only need to be loose here — `mix version` would do a stricter
+    # check, but we don't depend on Mix at the just layer.
+    if ! [[ "$NEW" =~ ^[0-9]+\.[0-9]+\.[0-9]+(-[A-Za-z0-9.-]+)?$ ]]; then
+        echo "ERROR: '$NEW' doesn't look like a semver version (e.g. 0.2.2 or 1.0.0-rc.1)" >&2
+        exit 1
+    fi
+
+    echo "Bumping $OLD → $NEW"
+    echo ""
+
+    # 1. mix.exs — the canonical version string
+    sed -i '' "s/version: \"$OLD\"/version: \"$NEW\"/" mix.exs
+    echo "  ✓ mix.exs"
+
+    # 2. github-page/index.html — the curl example
+    sed -i '' "s/ado-${OLD}-macos-aarch64/ado-${NEW}-macos-aarch64/g" github-page/index.html
+    echo "  ✓ github-page/index.html (Download binary curl example)"
+
+    # 3. README.md — the Publishing section's release flow + examples
+    #    (lines ~688–788, the publishing cheat-sheet). We replace
+    #    $OLD with $NEW; the rest of README shouldn't reference the
+    #    version, but if it does, the diff at the end will show it.
+    if [[ -f README.md ]]; then
+        sed -i '' "s/$OLD/$NEW/g" README.md
+        echo "  ✓ README.md (Publishing section)"
+    fi
+
+    echo ""
+    echo "Done. You still need to:"
+    echo ""
+    echo "  1. Add a CHANGELOG.md entry under '## [$NEW]'"
+    echo "       (see the [0.2.1] section as a template)"
+    echo "  2. Bump the 'Total project coverage is X% as of v$OLD' line in AGENTS.md"
+    echo "       if the coverage number has changed (only on v0.X.0 releases)"
+    echo "  3. Run \`mix format\` to normalize the diff"
+    echo "  4. Run \`just check\` to confirm CI is still green"
+    echo "  5. Commit, push, tag:"
+    echo "       git add -u && git commit -m 'release: v$NEW'"
+    echo "       git tag -a v$NEW -m 'Release $NEW'"
+    echo "       git push github main v$NEW"
+    echo "       (CI will build the binaries and create the GitHub Release)"
+    echo "  6. Run \`./scripts/npm-publish.sh $NEW\` locally to publish the npm packages"
+    echo ""
+    echo "Diff (review before committing):"
+    echo "─────────────────────────────────────────────────────────"
+    git --no-pager diff --stat
+    echo "─────────────────────────────────────────────────────────"
+    git --no-pager diff mix.exs github-page/index.html README.md | head -60