ADD 2.1.0 — two-agent roster maturity + persona-author v11 + flexible TDD + round-visible runs

Minor: the two-agent roster matures and the persona author learns from real
corpora; TDD flexes for non-coding tasks; every honest verify→build round
becomes engine-visible; the dogfood foundation completes its 2.0 migration.

• two-agent roster — add retires; add-worker runs every EXECUTION
  beat (direction · build · verify · persona) and add-advisor is the
  second mind serving EVERY beat (propose-plan · advise-midflight · refute)
  with a per-beat calibration map. The worker gains a mid-flight support
  fan-out for medium/large builds: non-overlapping §3-Scope slices,
  worktree isolation per support worker, the lead serializes git and re-runs
  the FULL suite on every return; the quality floor multiplies, never dilutes.
• persona-author skill — the static .add/personas/_template.md retires
  for a persona-author skill (contract · patterns · seeding references +
  two worked examples). Patterns grow 9 → 11 from a deep diagnosis of 13
  sample subagents and the 256-file teacher corpus: NEW numbers-you'd-defend
  (a named budget beats an adjective; fake precision is worse than none) and
  per-flow stance (what a lens LEADS with at build vs REFUSES at verify —
  the verify stance carries a default NEEDS-WORK verdict); seeding gains
  mine-the-gold / refuse-the-rot source guidance. All 6 live roster personas
  folded to patterns-v11.
• flexible TDD — §4 supports failing-first acceptance checks for
  non-coding kinds (docs · release · infra): verifiable pass/fail evidence,
  red before the artifact exists, green after — the red→green discipline
  holds; only the must-be-executable-code requirement is lifted. Guide,
  template, and book reframe; NO engine change (the kernel was already
  tolerant); 21 non-coding prose-guard tests retired dogfooding the policy.
• round-visible runs — every verify→build return trip is a recorded
  round: add.py phase build [--note "finding"] and every non-exhausted
  heal return increment an uncapped, observational tasks[slug].rounds
  (count + timestamped history, notes verbatim); status names round N;
  the route trace carries "rounds" beside "heals". Heal stays the
  cheat-classed, capped subset; rounds are the honest whole. --note off
  the build target refuses (phase_note_build_only).
• foundation-split — the dogfood board completes the 1.x→2.0 foundation
  migration this package's own migrate verb leaves to judgment: PROJECT.md
  322 → 63 lines (engine-read lines byte-identical), the pre-2.0 standing
  picture folded into the five .add/specs/ living specs with a per-bullet
  fold ledger — the worked example external 2.0 upgraders can follow.
• SKILL.md command cookbook — the skill router carries the common
  call recipes so agents skip the -h round-trip; README copy tightened
  (benefit-led highlights, honest tradeoffs, no dollar figures).

Retired (no CLI/install surface change): the add roster agent (superseded
by add-worker + add-advisor) and the static persona template (superseded by
the persona-author skill; init now creates an empty personas dir and the
hints point at the skill).