Improve form skills: validation, docs, round-trip consistency

form-compile: warn about unknown DSL keys in element definitions,
document stdCommand/command button keys and EPF-specific notes.

form-validate: check that form-level Title uses multilingual XML,
not plain text (which causes XDTO errors at build time).

form-add: warn about duplicate element names, clarify after-not-found
message when using into+after together.

form-info: show Title in header instead of Properties line, display
commands as DSL-friendly format (-> Name [cmd], -> Close [std])
instead of raw Form.Command/Form.StandardCommand paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/form-compile/scripts/form-compile.ps1

@@ -272,6 +272,47 @@ function Emit-Element {
 		return
 	}
 
+	# Validate known keys — warn about typos and unknown properties
+	$knownKeys = @{
+		# type keys
+		"group"=1;"input"=1;"check"=1;"label"=1;"labelField"=1;"table"=1;"pages"=1;"page"=1
+		"button"=1;"picture"=1;"picField"=1;"calendar"=1;"cmdBar"=1;"popup"=1
+		# naming & binding
+		"name"=1;"path"=1;"title"=1
+		# visibility & state
+		"visible"=1;"hidden"=1;"enabled"=1;"disabled"=1;"readOnly"=1
+		# events
+		"on"=1;"handlers"=1
+		# layout
+		"titleLocation"=1;"representation"=1;"width"=1;"height"=1
+		"horizontalStretch"=1;"verticalStretch"=1;"autoMaxWidth"=1;"autoMaxHeight"=1
+		# input-specific
+		"multiLine"=1;"passwordMode"=1;"choiceButton"=1;"clearButton"=1
+		"spinButton"=1;"dropListButton"=1;"markIncomplete"=1;"skipOnInput"=1;"inputHint"=1
+		# label/hyperlink
+		"hyperlink"=1
+		# group-specific
+		"showTitle"=1;"united"=1
+		# hierarchy
+		"children"=1;"columns"=1
+		# table-specific
+		"changeRowSet"=1;"changeRowOrder"=1;"header"=1;"footer"=1
+		"commandBarLocation"=1;"searchStringLocation"=1
+		# pages-specific
+		"pagesRepresentation"=1
+		# button-specific
+		"type"=1;"command"=1;"stdCommand"=1;"defaultButton"=1;"locationInCommandBar"=1
+		# picture/decoration
+		"src"=1
+		# cmdBar-specific
+		"autofill"=1
+	}
+	foreach ($p in $el.PSObject.Properties) {
+		if (-not $knownKeys.ContainsKey($p.Name)) {
+			Write-Warning "Element '$($el.$typeKey)': unknown key '$($p.Name)' — ignored. Check SKILL.md for valid keys."
+		}
+	}
+
 	$name = Get-ElementName -el $el -typeKey $typeKey
 	$id = New-Id