Daily run: Exponents & Roots content + growth playbook bootstrap

[DMDaudio]

Two things from the daily run land on this branch.

1. Content — Exponents & Roots (quant / arithmetic / exponents-roots)

First coverage of a taxonomy gap (no lesson or questions existed):

• 1 lesson — quant-arithmetic-exponents-roots: exponent rules, zero/negative exponents, roots as fractional exponents, simplifying radicals, same-base strategy for exponential equations; worked examples, common traps, key takeaways.
• 6 problem-solving questions (...-0017…0022), easy → hard: quotient rule; zero & negative exponents; power-of-a-power + product rule; simplifying/adding radicals; fractional exponents; same-base exponential equation.
• Rebuilt docs/data/content.json (now 38 questions, 9 lessons). Build clean, JSON valid.

All content is status: in-review, original work, schema-conformant.

2. Growth — user & contributor acquisition bootstrap

Adds growth/ as the durable home for growth, mirroring how curriculum.md guides content:

• growth/STRATEGY.md — canonical playbook: ICP, messaging pillars, channels/tactics, the daily growth-run operating procedure, metrics, guardrails, backlog.
• growth/LOG.md — running record so recurring runs don't repeat work.
• growth/posts/ — ready-to-publish drafts: an r/GMAT launch post, and a Show HN post (held until the bank is deeper). Each flags exactly what a human must do to publish.

Companion contributor-onboarding issues opened outside this PR: #13 (Start here), #14 (verify pass), #15 (in-site feedback link).

By design, external posting is left to a human — runs prepare everything up to "publish" and flag it.

Type of change

• New question(s)
• New lesson(s)
• Fix to existing content
• Tooling / docs / schema (growth playbook & drafts)

Author checklist

• Own original work — not copied from any real GMAT question or prep material.
• Front-matter follows CONTENT_SCHEMA.md (id matches filename; topic/subtopic in curriculum.md).
• Solved every question; exactly one correct answer each.
• Explanations help someone who got it wrong and name the trap.
• status is in-review; did not self-verify.

🤖 Generated with Claude Code

https://claude.ai/code/session_013vmmzouCLVAHnrES47GH7f