fix: Skip health check for remote HTTPS embedding APIs and wait for server in single-file indexing

Two fixes for KB indexing failures with Cloudflare Workers AI:
1. check_health() now short-circuits for HTTPS URLs (remote APIs like
   Cloudflare don't have /health endpoints and return 401/301/403 on
   probes, which were incorrectly treated as 'unreachable')
2. index_single_file_with_id() now calls wait_for_server(30) instead
   of immediately failing, giving the embedding server time to become
   ready

Root cause: EMBEDDING_SERVER_READY is a global flag. When the default
bot's local embedding server check fails, it blocks ALL bots including
those using remote HTTPS APIs that don't need a local health check.

botserver/src/core/kb/embedding_generator.rs

@@ -299,7 +299,16 @@ impl KbEmbeddingGenerator {
     }
 
     pub async fn check_health(&self) -> bool {
-        // Strategy: try /health endpoint on BASE URL first.
+        // Remote HTTPS APIs (Cloudflare Workers AI, OpenAI, etc.) are assumed available
+        // — they don't have /health endpoints and return 401/403/301 on probe.
+        // Only local servers need TCP health checks.
+        if self.config.embedding_url.starts_with("https://") {
+            info!("Embedding server is remote HTTPS API ({}), assuming available", self.config.embedding_url);
+            set_embedding_server_ready(true);
+            return true;
+        }
+
+        // Strategy for local servers: try /health endpoint on BASE URL first.
         // - 200 OK → local server with health endpoint, ready
         // - 404/405 etc → server is reachable but has no /health (remote API or llama.cpp)
         // - Connection refused/timeout → server truly unavailable

botserver/src/core/kb/kb_indexer.rs

@@ -549,12 +549,14 @@ pub async fn index_single_file_with_id(
     kb_name: &str,
     file_path: &Path,
     document_id: Option<&str>,
-) -> Result<IndexingResult> {
-    if !is_embedding_server_ready() {
-        return Err(anyhow::anyhow!(
-            "Embedding server not available. Cannot index file."
-        ));
-    }
+    ) -> Result<IndexingResult> {
+        if !is_embedding_server_ready() {
+            if !self.embedding_generator.wait_for_server(30).await {
+                return Err(anyhow::anyhow!(
+                    "Embedding server not available. Cannot index file."
+                ));
+            }
+        }
 
     if !self.check_qdrant_health().await.unwrap_or(false) {
         return Err(anyhow::anyhow!(