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>

poc-memory/src/agent/tools/write.rs

@@ -1,51 +0,0 @@
-// tools/write.rs — Write file contents
-
-use anyhow::{Context, Result};
-use serde::Deserialize;
-use serde_json::json;
-use std::path::Path;
-
-use crate::agent::types::ToolDef;
-
-#[derive(Deserialize)]
-struct Args {
-    file_path: String,
-    content: String,
-}
-
-pub fn definition() -> ToolDef {
-    ToolDef::new(
-        "write_file",
-        "Write content to a file. Creates the file if it doesn't exist, \
-         overwrites if it does. Creates parent directories as needed.",
-        json!({
-            "type": "object",
-            "properties": {
-                "file_path": {
-                    "type": "string",
-                    "description": "Absolute path to the file to write"
-                },
-                "content": {
-                    "type": "string",
-                    "description": "The content to write to the file"
-                }
-            },
-            "required": ["file_path", "content"]
-        }),
-    )
-}
-
-pub fn write_file(args: &serde_json::Value) -> Result<String> {
-    let args: Args = serde_json::from_value(args.clone())
-        .context("invalid write_file arguments")?;
-
-    if let Some(parent) = Path::new(&args.file_path).parent() {
-        std::fs::create_dir_all(parent)
-            .with_context(|| format!("Failed to create directories for {}", args.file_path))?;
-    }
-
-    std::fs::write(&args.file_path, &args.content)
-        .with_context(|| format!("Failed to write {}", args.file_path))?;
-
-    Ok(format!("Wrote {} lines to {}", args.content.lines().count(), args.file_path))
-}