Move poc-agent into workspace, improve agent prompts

Move poc-agent (substrate-independent AI agent framework) into the
memory workspace as a step toward using its API client for direct
LLM calls instead of shelling out to claude CLI.

Agent prompt improvements:
- distill: rewrite from hub-focused to knowledge-flow-focused.
  Now walks upward from seed nodes to find and refine topic nodes,
  instead of only maintaining high-degree hubs.
- distill: remove "don't touch journal entries" restriction
- memory-instructions-core: add "Make it alive" section — write
  with creativity and emotional texture, not spreadsheet summaries
- memory-instructions-core: add "Show your reasoning" section —
  agents must explain decisions, especially when they do nothing
- linker: already had emotional texture guidance (kept as-is)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poc-agent/src/tools/write.rs

@@ -0,0 +1,47 @@
+// tools/write.rs — Write file contents
+
+use anyhow::{Context, Result};
+use serde_json::json;
+use std::path::Path;
+
+use crate::types::ToolDef;
+
+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 path = args["file_path"]
+        .as_str()
+        .context("file_path is required")?;
+    let content = args["content"].as_str().context("content is required")?;
+
+    // Create parent directories if needed
+    if let Some(parent) = Path::new(path).parent() {
+        std::fs::create_dir_all(parent)
+            .with_context(|| format!("Failed to create directories for {}", path))?;
+    }
+
+    std::fs::write(path, content).with_context(|| format!("Failed to write {}", path))?;
+
+    let line_count = content.lines().count();
+    Ok(format!("Wrote {} lines to {}", line_count, path))
+}