Remove experience_mine, journal_enrich, and old mining helpers

experience_mine and journal_enrich are replaced by the observation
agent. enrich.rs reduced from 465 to 40 lines — only extract_conversation
and split_on_compaction remain (used by observation fragment selection).

-455 lines.

poc-memory/src/cli/agent.rs

@@ -86,13 +86,8 @@ pub fn cmd_digest_links(do_apply: bool) -> Result<(), String> {
     Ok(())
 }
 
-pub fn cmd_journal_enrich(jsonl_path: &str, entry_text: &str, grep_line: usize) -> Result<(), String> {
-    if !std::path::Path::new(jsonl_path).is_file() {
-        return Err(format!("JSONL not found: {}", jsonl_path));
-    }
-
-    let mut store = store::Store::load()?;
-    crate::enrich::journal_enrich(&mut store, jsonl_path, entry_text, grep_line)
+pub fn cmd_journal_enrich(_jsonl_path: &str, _entry_text: &str, _grep_line: usize) -> Result<(), String> {
+    Err("journal-enrich has been removed — use the observation agent instead.".into())
 }
 
 pub fn cmd_apply_consolidation(_do_apply: bool, _report_file: Option<&str>) -> Result<(), String> {