0.7.0 — vocabulary 14: palette roles, sprite v2, two-tone patterns, dither

Palette roles and retro looks: sprite format v2 with the hero character (spec 020, #103), a
second pattern tone (spec 019, #97), and ordered-dither scenes (spec 021, #107), with Game Boy,
SNES and DOS adventure showcase loops. No existing reference frame moved.

• A spec may carry a roles map of named colours (up to 16), used only in creative mode.
  Outside creative mode every role falls back to a grey, so output stays monochrome.
• sprite gains hero, a 16 × 20 character whose ten parts (hair, skin, eyes, gold trim,
  cloak, boots and more) take their colours from roles. Built-in characters may now
  declare a per-letter palette (format v2, up to 32 × 48); mascot, bot and ghost are
  unchanged.
• sanitizeRoles is exported. npm run verify now checks that built-in characters are
  well-formed, and the palette gate accepts mixes of the background with a declared role.
• grid and checker patterns: the letter b draws a second tone, coloured by roles.fg2 in
  creative mode and mid grey otherwise (spec 019, #97). Patterns without b are unchanged.
• dither: an ordered (Bayer) dither gradient through up to six palette roles in a region,
  for DOS/VGA-style skies, ground, props and UI bars (spec 021, #107). caption gains
  margin, and a spec may declare pixelAspect (recorded in the command-line manifest, never
  changing a pixel). A dos-adventure showcase loop shows the look.
• Constitution 4.0.0: Principle III now reads "palette roles" instead of only background,
  foreground and accent. Constitution 4.1.0: the palette
  gate accepts a role mixed with both background and foreground, as it does the accent.
  Constitution 4.2.0: pixelAspect joins the format.