feat(runtime): replace tokio+reqwest with asupersync async runtime

- Add HTTP adapter layer (src/http.rs) wrapping asupersync h1 client
- Migrate gitlab client, graphql, and ollama to HTTP adapter
- Swap entrypoint from #[tokio::main] to RuntimeBuilder::new().block_on()
- Rewrite signal handler for asupersync (RuntimeHandle::spawn + ctrl_c())
- Migrate rate limiter sleeps to asupersync::time::sleep(wall_now(), d)
- Add asupersync-native HTTP integration tests
- Convert timeline_seed_tests to RuntimeBuilder pattern

Phases 1-3 of asupersync migration (atomic: code won't compile without all pieces).

src/core/shutdown.rs

@@ -1,16 +1,18 @@
 use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
 
+use asupersync::runtime::RuntimeHandle;
+
 /// Spawn a background task that listens for Ctrl+C.
 ///
 /// First press: cancels `signal` and prints an interrupt message.
 /// Second press: force-exits with code 130.
-pub fn install_ctrl_c_handler(signal: ShutdownSignal) {
-    tokio::spawn(async move {
-        let _ = tokio::signal::ctrl_c().await;
+pub fn install_ctrl_c_handler(handle: &RuntimeHandle, signal: ShutdownSignal) {
+    handle.spawn(async move {
+        let _ = asupersync::signal::ctrl_c().await;
         eprintln!("\nInterrupted, finishing current batch... (Ctrl+C again to force quit)");
         signal.cancel();
-        let _ = tokio::signal::ctrl_c().await;
+        let _ = asupersync::signal::ctrl_c().await;
         std::process::exit(130);
     });
 }