v2.3.0

A focused release that brings alt-chord training to drill and book
modes, adds an interactive chordgen add command for one-off word
additions, and ships a long list of alt-generation cleanups so the
default chords.csv is noticeably less noisy.

Highlights

• Alt chords show up everywhere. Drill and book modes now
  surface alt1/alt2/alt3 inflections (e.g. sets, setting,
  settings for set) — they inherit their base row's FSRS
  mastery, get the slot-suffixed chord display (au → au1), and
  light up the alt1 alt2 alt3 indicator below the keyboard.
  Disable via drill.include_alts: false.
• chordgen add WORDS... — interactive one-off additions to
  chords.csv with a live red/green chord prompt, inline
  rejection reasons, auto-detected category, and reserved-row
  pinning so future chordgen gen runs leave the chosen chord
  alone.
• always_show_chords for drill and book. Reveal chords
  beneath every word from the start, not just on a stumble. Off
  by default in both modes.
• Cleaner alt generation by default. Six families of bogus
  alts (contraction-stem residue, subtitle artefacts, mis-tagged
  interjections, non-gradable adjectives, double-pluralised
  rows, irregular-verb conjugations) no longer leak into
  chords.csv from chordgen setup / chordgen gen.

See the changelog for more details