merge poc-agent into poc-memory as agent/ module

Eliminates the circular dependency between poc-agent and poc-memory by
moving all poc-agent source into poc-memory/src/agent/. The poc-agent
binary now builds from poc-memory/src/bin/poc-agent.rs using library
imports. All poc_agent:: references updated to crate::agent::.

poc-agent/ directory kept for now (removed from workspace members).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

poc-memory/src/agent/mod.rs

@@ -0,0 +1,39 @@
+#[macro_export]
+macro_rules! dbglog {
+    ($($arg:tt)*) => {{
+        use std::io::Write;
+        if let Ok(mut f) = std::fs::OpenOptions::new()
+            .create(true).append(true)
+            .open("/tmp/poc-debug.log")
+        {
+            let _ = writeln!(f, $($arg)*);
+        }
+    }};
+}
+
+// agent/ — interactive agent and shared infrastructure
+//
+// Merged from the former poc-agent crate. Contains:
+// - api/       — LLM API backends (OpenAI-compatible, Anthropic)
+// - types      — Message, ToolDef, ChatRequest, etc.
+// - tools/     — tool definitions and dispatch
+// - ui_channel — streaming UI communication
+// - runner     — the interactive agent loop
+// - cli, config, context, dmn, identity, log, observe, parsing, tui
+
+pub mod api;
+pub mod types;
+pub mod tools;
+pub mod ui_channel;
+pub mod journal;
+
+pub mod runner;
+pub mod cli;
+pub mod config;
+pub mod context;
+pub mod dmn;
+pub mod identity;
+pub mod log;
+pub mod observe;
+pub mod parsing;
+pub mod tui;