Seed content: Number Properties batch (+5 questions, +1 lesson)

[DMDaudio]

What does this PR add or change?

Adds the first Number Properties content to the bank — a subtopic that previously had a single question and no lesson at all. This is a coherent study session covering the Quant number-properties topic top-to-bottom, with an easy → hard difficulty progression.

New lesson

• quant-number-properties-remainders — "Remainders & Modular Thinking" (the division identity, multiplying/adding remainders, combining two moduli, common traps).

New questions

• quant-number-properties-remainders-0017 (easy) — remainder of 3n given n ≡ 4 (mod 7).
• quant-number-properties-remainders-0018 (hard) — combine n ≡ 3 (mod 5) and n ≡ 4 (mod 7) to find the remainder mod 35.
• quant-number-properties-odds-evens-signs-0019 (medium) — must-be-true parity given an odd product.
• quant-number-properties-factors-0020 (medium) — divisor count of the LCM of 12 and 18.
• quant-number-properties-factors-0021 (hard) — how many divisors of 2⁴·3²·5 are multiples of 10.

Rebuilt docs/data/content.json via node scripts/build.mjs (now 37 questions, 9 lessons; builder reports no 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.

🤖 Generated with Claude Code

https://claude.ai/code/session_01TWGyV3Vvv1hxzHHHP1j7nr

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