feat(functions push): add --manifest path for non-SDK function types

The runner-based push path can only ship function types the Braintrust
SDK exposes builders for: tools, scorers, prompts, parameters. Topics-
pipeline types (facet, classifier) and inline-quickjs preprocessors
have no SDK builder, so AI-agent workflows that author lenses cannot
push them through `bt`.

`--manifest <path>` accepts a JSON object or array of objects matching
the wire shape `/insert-functions` already accepts (the same endpoint
`bt topics config enable` uses to create classifier functions). The
manifest path bypasses the runner entirely; auth, project resolution,
and `--if-exists` flow through the existing helpers.

Mutually exclusive with `--file`, positional file paths, `--runner`,
`--language`, `--requirements`, `--tsconfig`, and `--external-packages`,
since none of those apply when the SDK runner is skipped.

Closes #149.

Author: imen-kedir

src/functions/mod.rs

@@ -270,6 +270,18 @@ pub(crate) struct PushArgs {
     )]
     pub file_flag: Vec<PathBuf>,
 
+    /// JSON manifest file with one or more raw function definitions.
+    /// Skips the SDK runner; the manifest is posted directly to /insert-functions.
+    /// Use this for function types the SDK doesn't expose builders for
+    /// (preprocessor with inline-quickjs runtime, facet, classifier).
+    #[arg(
+        long = "manifest",
+        env = "BT_FUNCTIONS_PUSH_MANIFEST",
+        value_name = "PATH",
+        conflicts_with_all = ["files", "file_flag", "runner", "language", "requirements", "tsconfig", "external_packages"]
+    )]
+    pub manifest: Option<PathBuf>,
+
     /// Behavior when a function with the same slug already exists.
     #[arg(
         long = "if-exists",
@@ -687,6 +699,35 @@ mod tests {
         assert!(msg.contains("--type"));
     }
 
+    #[test]
+    fn push_manifest_flag_parses() {
+        let _guard = test_lock();
+        let parsed =
+            parse(&["functions", "push", "--manifest", "fn.json"]).expect("parse push manifest");
+        let FunctionsCommands::Push(push) = parsed.command.expect("subcommand") else {
+            panic!("expected push command");
+        };
+        assert_eq!(
+            push.manifest,
+            Some(std::path::PathBuf::from("fn.json")),
+            "manifest path should be parsed"
+        );
+        assert!(push.files.is_empty());
+        assert!(push.file_flag.is_empty());
+    }
+
+    #[test]
+    fn push_manifest_conflicts_with_file_path() {
+        let _guard = test_lock();
+        let err = parse(&["functions", "push", "--manifest", "fn.json", "extra.ts"])
+            .expect_err("manifest+file path should conflict");
+        let msg = err.to_string();
+        assert!(
+            msg.contains("manifest") || msg.contains("--manifest") || msg.contains("conflict"),
+            "expected conflict-related error, got: {msg}"
+        );
+    }
+
     #[test]
     fn top_level_type_flag_still_parses_for_functions_namespace() {
         let _guard = test_lock();