chore(docs, platform): finalize migration guides for Exposed 1.0.0 and Ktor 3.4.0 upgrades

- Updated Exposed migration guide with detailed breaking changes, migration steps, test matrix, and rollback plan.
- Published technical analysis for transitioning to Ktor 3.4.0, including API improvements and routing OpenAPI integration.
- Aligned `platform-bom` with upgraded dependencies: `exposed` 1.0.0 and `ktor` 3.4.0.
- Introduced `ktor-server-routing-openapi` dependency for dynamic API documentation support.

platform/platform-bom/build.gradle.kts

@@ -63,6 +63,8 @@ dependencies {
         // --- Jackson Modules ---
         api(libs.jackson.module.kotlin)
         api(libs.jackson.datatype.jsr310)
+        // --- Ktor OpenAPI (runtime-based docs require explicit routing-openapi in 3.4.0) ---
+        api("io.ktor:ktor-server-routing-openapi:${libs.versions.ktor.get()}")
         // --- Testcontainers ---
         // Testcontainers Bundle kann nicht direkt in constraints verwendet werden
         api(libs.testcontainers.core)