v1.2.0 — Agent ergonomics + kraft/studio themes

Authoring-path release. The runtime (ifbase.js) is unchanged; ifbase.css gains two theme presets.

Added

• tools/build.mjs — authoring CLI. node tools/build.mjs spec.json --out path/to/form.html builds a form to any path, with --assets inline|absolute|relative, --theme, --hue. Replaces the per-agent hand-substitution of the spec into template.html.
• Self-contained forms by default. --assets inline embeds ifbase.css/ifbase.js — one portable file that opens anywhere and survives emailing.
• validateSpec(). loadSpec now rejects malformed specs (unknown type, duplicate id incl. branch ids, branch on non-radio, nested branches, segmented 2–5, priority-rank ≥2, empty sections) with a clear message instead of a silent broken form.
• kraft and studio theme presets shipped. Both were reserved enum values with no CSS; now implemented and passing the accessibility audit (zero axe violations on both layouts).
• tools/ documented in SKILL.md as the preferred authoring path, plus a defaults-by-type table.

Verified

13/13 specs render with zero console errors; all five theme presets pass axe with zero violations.