Seed content: Quant exponents & roots + remainders (2 lessons, 14 questions)

[DMDaudio]

What does this PR add or change?

Adds two previously-uncovered but high-frequency Quant subtopic bundles.

1. Arithmetic → exponents-roots

• 1 lesson (quant-arithmetic-exponents-roots) — power rules, negative/zero/fractional exponents, radical simplification, factoring common powers.
• 7 problem-solving questions (0017–0023), easy→hard: power rules, negative/zero exponents, same-base equations, fractional exponents, radicals, factoring a sum of equal powers, ratio of powers.

2. Number Properties → remainders (new in this update)

• 1 lesson (quant-number-properties-remainders) — the division identity (n = dq + r), combining remainders across sums and products (reduce again at the end), power cyclicity / units digits, and simultaneous-condition (lcm) problems.

• 7 problem-solving questions (0024–0030) with an easy→hard progression:

  • 0024 (easy) — remainder of a sum
  • 0025 (easy) — translating quotient/remainder via (n = dq + r)
  • 0026 (medium) — remainder of a product
  • 0027 (medium) — remainder of a power via units-digit cyclicity
  • 0028 (medium) — two simultaneous remainder conditions, least value
  • 0029 (hard) — reasoning from the remainder of (n^2) back to (n)
  • 0030 (hard) — combining mod-4 and mod-6 conditions to get the remainder mod 12

• Every question's distractors are keyed to a specific common error (e.g. forgetting the final reduction, adding remainders when the numbers are multiplied, swapping quotient/remainder, assuming (n) and (n^2) share a remainder, misreading a cycle position of 0).

• Choice-level and body math is wrapped in \( \) / \[ \] for KaTeX rendering.

• Rebuilt docs/data/content.json — now 46 questions, 10 lessons; node scripts/build.mjs reports zero warnings.

Type of change

• New question(s)
• New lesson(s)
• Fix to existing content (answer / explanation / tag)
• Tooling / docs / schema

Author checklist

• This is my own original work — not copied or paraphrased from any real GMAT question or prep material.
• Front-matter follows CONTENT_SCHEMA.md (id matches the filename; topic/subtopic exist in curriculum.md).
• I solved every question myself and confirmed exactly one answer choice is correct.
• Each explanation would help someone who got the question wrong, and names the trap where relevant.
• status is in-review. I did not set my own content to verified.

For reviewers

• I solved the question(s) without reading the keyed answer first and got the same answer.
• Exactly one choice is correct; distractors are plausible.
• Explanation and tags (section / topic / difficulty) are accurate.
• If approving: bumped status to verified and added my handle to reviewers.

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