flatten: move poc-memory contents to workspace root

No more subcrate nesting — src/, agents/, schema/, defaults/, build.rs
all live at the workspace root. poc-daemon remains as the only workspace
member. Crate name (poc-memory) and all imports unchanged.

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

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;