refactor: migrate FlowTemplateParserTest to KosliTemplateParser and delete deprecated parser

[MaximumTrainer]

Background

FlowTemplateParser was deprecated in favour of the Spring-managed KosliTemplateParser (which adds ifCondition support on attestations). The parser is marked @Deprecated(level = DeprecationLevel.WARNING) but cannot be deleted while FlowTemplateParserTest still references it.

Tasks

• Update FlowTemplateParserTest to use KosliTemplateParser instead of FlowTemplateParser
• Delete backend/src/main/kotlin/com/factstore/application/FlowTemplateParser.kt
• Verify ./gradlew test passes with zero deprecation warnings

Files

• backend/src/main/kotlin/com/factstore/application/FlowTemplateParser.kt
• backend/src/test/kotlin/com/factstore/FlowTemplateParserTest.kt