core: refactor tool system to remove agent context from initialization (#21052)

packages/opencode/specs/v2/keymappings.md

@@ -0,0 +1,10 @@
+# Keybindings vs. Keymappings
+
+Make it `keymappings`, closer to neovim. Can be layered like `<leader>abc`. Commands don't define their binding, but have an id that a key can be mapped to like
+
+```ts
+{ key: "ctrl+w", cmd: string | function, description }
+```
+
+_Why_
+Currently its keybindings that have an `id` like `message_redo` and then a command can use that or define it's own binding. While some keybindings are just used with `.match` in arbitrary key handlers and there is no info what the key is used for, except the binding id maybe. It also is unknown in which context/scope what binding is active, so a plugin like `which-key` is nearly impossible to get right.