feat: add automatic greeting upon connection (#42)

### Explanation

_No response_

### Issue

Closes #23

### Attestations

- [ ] I have read and agree to the [Code of Conduct](https://docs.nhcarrigan.com/community/coc/)
- [ ] I have read and agree to the [Community Guidelines](https://docs.nhcarrigan.com/community/guide/).
- [ ] 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.
- [ ] My pull request uses an appropriate title, matching the conventional commit standards.
- [ ] 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: #42
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/stores/config.ts

@@ -10,6 +10,8 @@ export interface HikariConfig {
   mcp_servers_json: string | null;
   auto_granted_tools: string[];
   theme: Theme;
+  greeting_enabled: boolean;
+  greeting_custom_prompt: string | null;
 }
 
 const defaultConfig: HikariConfig = {
@@ -19,6 +21,8 @@ const defaultConfig: HikariConfig = {
   mcp_servers_json: null,
   auto_granted_tools: [],
   theme: "dark",
+  greeting_enabled: true,
+  greeting_custom_prompt: null,
 };
 
 function createConfigStore() {