Form names any AABA arrangement ThirtyTwoBarAABA regardless of section length, and NamedForm.VerseChorus can never be produced #384

What's wrong

The music-analysis spec defines named-form recognition from the section-letter pattern as follows:

https://github.com/ktsu-dev/Semantics/blob/ea623ae52e34c5297f5d1d157a48b52f4061cc49/docs/superpowers/specs/2026-07-01-music-analysis-aggregate-design.md#L238-L260

ThirtyTwoBarAABA = AABA (with the four sections each ~8 bars) … enum NamedForm { ThirtyTwoBarAABA, TwelveBarBlues, VerseChorus, … }

Semantics.Music/Form.cs implements only part of this:

1. The AABA bar-length check is missing. RecognizePattern maps the string "AABA" straight to NamedForm.ThirtyTwoBarAABA (Form.cs ~L106-109). It never looks at Section.Bars, although Form.Of has the sections in hand.
   • Four 2-bar sections in an A A B A order are reported as a "32-bar AABA" form, which is 8 bars long.
   • Form.Parse("AABA") has no bar information at all, so it also returns ThirtyTwoBarAABA. The parse-only path should arguably stay as it is, or return a less specific name, but that choice needs to be made on purpose.
2. NamedForm.VerseChorus can never be produced. It is declared in NamedForm.cs:15, but neither RecognizePattern nor Form.Of returns it. The spec lists it in the enum but never gives it a recognition rule.
   • A consumer that switches over NamedForm gets an arm that can never fire.
   • A verse/chorus song such as Verse, Chorus, Verse, Chorus, Bridge, Chorus (the spec's own example, L232) comes out as Unknown.

(The 12-bar blues half of this spec section, which counts events rather than bars, is already tracked in #317 and is not part of this issue.)

What exists today

• Semantics.Music/Form.cs: Of builds the letter pattern from IsSameStructure groups; RecognizePattern does a pure string switch.
• Semantics.Music/Section.cs:26: Section.Bars already exists, derived from Progression.TotalBars, so the data needed for the check is available.
• Semantics.Test/Music/FormTests.cs: Of_ExtractsAABAPattern_AndNamesThirtyTwoBarForm uses short sections and still expects ThirtyTwoBarAABA.

Acceptance criteria

• Form.Of returns ThirtyTwoBarAABA only when the pattern is AABA and each of the four sections is about 8 bars long. Pick and document a tolerance; exactly 8 is the simplest choice. Otherwise it falls through to the generic result for that pattern (Unknown).
• Decide what Form.Parse("AABA") returns when it has no bar data, and document that in the XML docs.
• VerseChorus either:
  • gets a recognition rule based on SectionType, for example the arrangement alternates sections typed Verse and Chorus with at least two of each, allowing an optional Bridge/Intro/Outro, plus a test; or
  • is removed from NamedForm. That is a breaking change and should be tagged [major].
• Tests:
  • AABA made of 8-bar sections gives ThirtyTwoBarAABA.
  • AABA made of 2-bar sections gives something other than ThirtyTwoBarAABA.
  • The spec's verse/chorus example gives VerseChorus, if that option is chosen.

Dependencies

None. This can land independently of #317, although both touch Form.Of and could share a PR.