tools: each module exports only tool() or tools(), nothing else

Every tool module now has a clean interface:
- read, write, edit, grep, glob, bash, vision: pub fn tool() -> Tool
- web: pub fn tools() -> [Tool; 2]
- memory: pub fn memory_tools() -> Vec<Tool>
- channels: pub fn tools() -> Vec<Tool>
- control: pub fn tools() -> Vec<Tool>

Definition and handler functions are private to each module.
mod.rs::tools() just chains the module exports.

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

src/agent/tools/vision.rs

@@ -21,7 +21,7 @@ struct Args {
 
 fn default_lines() -> usize { 50 }
 
-pub(super) fn definition() -> ToolDef {
+fn definition() -> ToolDef {
     ToolDef::new(
         "view_image",
         "View an image file or capture a tmux pane screenshot. \
@@ -48,8 +48,12 @@ pub(super) fn definition() -> ToolDef {
     )
 }
 
+pub fn tool() -> super::Tool {
+    super::Tool { def: definition(), handler: |_a, v| Box::pin(async move { view_image_text(&v) }) }
+}
+
 /// Text-only version for the Tool registry.
-pub fn view_image_text(args: &serde_json::Value) -> anyhow::Result<String> {
+fn view_image_text(args: &serde_json::Value) -> anyhow::Result<String> {
     let output = view_image(args)?;
     Ok(output.text)
 }