fix: config hot reload support for dev server

[rohilsurana]

Problem

When running `chronicle dev`, changes to `chronicle.yaml` are not picked up. The config is loaded once at startup via `loadConfig()` and cached. Site owners must restart the dev server after any config change (adding content dirs, changing theme, updating navigation, etc.).

Expected Behavior

The dev server should watch `chronicle.yaml` for changes and:

1. Re-validate the config
2. Re-symlink content directories if content entries changed
3. Trigger a full page reload (not HMR — config changes are structural)
4. Log what changed in the terminal

Note

Vite already supports watching arbitrary files and triggering reload. The main work is re-running the config loader and content symlinking on change.