fix(help): pptx shape spacing is documented in the wrong unit

[lukiod]

Fixes #291. Help text only, 3 lines, no code change.

schemas/help/pptx/shape.json described spacing as 1/100 pt and offered --prop spacing=200 as the example. The setter parses points and multiplies by 100, so following the printed example writes spc="20000", which is 200pt of letter spacing.

Validation: authoritative reference (CONTRIBUTING rule 2, option 3)

The code is the reference here, since the defect is that the docs disagree with it.

src/officecli/Handlers/Pptx/PowerPointHandler.ShapeProperties.cs:1502:

case "spacing" or "charspacing" or "letterspacing" or "spc":
{
    // Character spacing in points (e.g. "2" = +2pt, "-1" = -1pt)
    // Stored as 1/100th of a point in OOXML
    ...
    var spcVal = (int)(spcDbl * 100);

Its own error message says Expected a finite number in points (e.g. 2, -1, 0.5).

schemas/help/pptx/run.json already documents the same OOXML attribute correctly ("character spacing in points. Stored as 1/100 pt in OOXML"), so the two help files contradicted each other for one attribute. This aligns shape.json with both the code and run.json.

The new examples are spacing=2 and spacing=-0.5, the latter because the setter accepts fractional points and negatives tighten.

Not changed

"readback": "integer" on this property looks questionable too, since readback is described elsewhere as the point value and points can be fractional. I did not trace the readback path, so I left it rather than guess. Happy to open a separate issue if that is worth checking.