feat: add chat modes and interrupt feature (#46)

### Explanation

_No response_

### Issue

Closes #40

### Attestations

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- [ ] My contribution complies with the [Contributor Covenant](https://docs.nhcarrigan.com/dev/covenant/).

### Dependencies

- [ ] I have pinned the dependencies to a specific patch version.

### Style

- [ ] I have run the linter and resolved any errors.
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- [ ] My scope of feat/fix/chore/etc. correctly matches the nature of changes in my pull request.

### Tests

- [ ] My contribution adds new code, and I have added tests to cover it.
- [ ] My contribution modifies existing code, and I have updated the tests to reflect these changes.
- [ ] All new and existing tests pass locally with my changes.
- [ ] Code coverage remains at or above the configured threshold.

### Documentation

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### Versioning

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Reviewed-on: #46
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/stores/messageMode.ts

@@ -0,0 +1,20 @@
+import { writable } from "svelte/store";
+
+// Default to chat mode
+const messageModeStore = writable<string>("chat");
+
+export const messageMode = {
+  subscribe: messageModeStore.subscribe,
+  set: (mode: string) => {
+    console.log("Setting message mode to:", mode);
+    messageModeStore.set(mode);
+  },
+  reset: () => messageModeStore.set("chat"),
+};
+
+// Helper to get current mode
+export function getCurrentMode(): string {
+  let currentMode = "chat";
+  messageMode.subscribe((mode) => (currentMode = mode))();
+  return currentMode;
+}