feat(phase9): LlmEngine::extract_content_tags + smoke test

Added as a method on LlmEngine alongside cleanup_text and
extract_tasks; same render_chat_prompt -> generate -> parse pattern.
Truncates the transcript to its trailing 2000 chars on a UTF-8 char
boundary, runs at temperature 0.0 with the CONTENT_TAGS_GRAMMAR GBNF,
and re-validates intent against INTENT_CLOSED_SET to catch the
unlikely grammar bypass case. max_tokens 96 is enough for the JSON
envelope. Smoke test gated on KON_LLM_TEST_MODEL like the existing
smoke.rs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/llm/tests/content_tags_smoke.rs

@@ -0,0 +1,48 @@
+//! Smoke test for Phase 9 LlmEngine::extract_content_tags.
+//!
+//! Gated behind the same `KON_LLM_TEST_MODEL` env var as the existing
+//! smoke.rs test so neither runs in default `cargo test` runs (model
+//! load is heavy). Run explicitly with:
+//!
+//!     KON_LLM_TEST_MODEL=/path/to/model.gguf cargo test -p kon-llm \
+//!         --test content_tags_smoke -- --nocapture
+
+use std::env;
+use std::path::PathBuf;
+
+use kon_llm::{is_valid_intent, LlmEngine, LlmModelId};
+
+#[test]
+fn extract_content_tags_returns_valid_pair() {
+    let model_path = match env::var("KON_LLM_TEST_MODEL") {
+        Ok(path) => PathBuf::from(path),
+        Err(_) => {
+            eprintln!("KON_LLM_TEST_MODEL not set — skipping");
+            return;
+        }
+    };
+
+    let engine = LlmEngine::new();
+    engine
+        .load_model(LlmModelId::Qwen3_1_7B_Q4, &model_path, true)
+        .expect("load model");
+
+    let transcript = "Tomorrow I need to run through the grant application one more time \
+                      and make sure the figures add up. I also need to book a slot with \
+                      Rachmann for the Mac test and email Andrew about the meeting window.";
+    let tags = engine
+        .extract_content_tags(transcript)
+        .expect("extract_content_tags");
+
+    assert!(tags.topic.len() >= 3, "topic present: {tags:?}");
+    assert!(
+        tags.topic
+            .chars()
+            .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-'),
+        "topic lowercase + slugged: {tags:?}",
+    );
+    assert!(
+        is_valid_intent(&tags.intent),
+        "intent in closed set: {tags:?}",
+    );
+}