Skill audit report

mc-development Audit report.

Thematic development (乐思发展层) - what the theme is and what each section does with it. Owns `material` (motif, character, stated_in) and `form[].development`, a closed set of ten operations (repeat/sequence/extend/contract/fragment/vary/augment/counterpoint/new/recap). Covers the line between developing and piling up, each operation with its criterion and cost, motive-to-phrase construction, phrase-to-section-to-whole (overlap, supplement, recapitulation), the variation branch, and where it all lands in a pop song. Use when every section sounds like new material, when a song feels loose, when deciding what the second verse or the last chorus should do, or when filling `material` and `form[].development` in an ARR-SPEC. 乐思发展、动机、主题材料、每段都在写新东西、扩充、减缩、裁截、模进、变奏、再现。