fix(ci): restrict workflow to PRs and improve release tagging

Restrict the CI pipeline to pull request events only by removing the unconfigured push trigger and eliminating a duplicate pull_request block in the workflow file. Update the Makefile to suppress stderr from the aichat command and introduce a fallback release tag message for robust version tagging. Additionally, bump the obikmer crate version to 1.1.19.

src/Cargo.lock

@@ -1704,7 +1704,7 @@ dependencies = [
 
 [[package]]
 name = "obikmer"
-version = "1.1.18"
+version = "1.1.19"
 dependencies = [
  "clap",
  "csv",

src/obikmer/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "obikmer"
-version = "1.1.18"
+version = "1.1.19"
 edition = "2024"
 
 [[bin]]