feat: edit user messages (#170)

Add implementation of the Edit user message feature.

Similar to ChatGPT, when the user edits a message, the old response is
replaced with the new one and all newer messages are deleted so that the
edited message is the last in the conversation.

For example, in this conversation:

```
User: Prompt 1
AI: Response 1
User: Prompt 2
AI: Response 2
```

If the user edits `Prompt 1`, then `Response 1` is replaced for the new
response, and `Prompt 2` and `Response 2` get removed from the session
history.

---------

Co-authored-by: Fernando Maclen <[email protected]>

fix: can manually (or opt-in to automatically) check for updates (#159)

- Can opt-in to check for updates automatically
- If enabled, it checks for updates once a week
- Can manually check for updates regardless of auto-update setting
- It shows update instructions based on the Hollama server environment

fix: fix scrolling after submitting a prompt (#163)

This bug was happening because `handleCompletion` sets `isCompletionInProgress` to `true`, which makes
the `...` message visible:

```svelte
{#if isCompletionInProgress}
  <Article message={{ role: 'assistant', content: completion || '...' }} />
{/if}
```

It seems that this render occurs after the `scrollToBottom` invocation. 

I fixed it by using the `requestAnimationFrame` [function](https://developer.mozilla.org/en-US/docs/Web/API/Window/requestAnimationFrame),
which schedules the scroll action to occur in the next frame after the browser has completed its current rendering tasks.

fix: abort completion if user confirms to change the current session (#…

…145)

* fix manually aborting a session, it was not working
* if the user clicks on another session while a completion is being
written, they have to confirm
* if the user confirms, the completion is aborted before changing the
session

---------

Co-authored-by: Fernando Maclen <[email protected]>

feat: download Ollama models from UI (#157)

Closes #142

fix: sort the available model list alphabetically (#120)

Closes #104

- sort models received from ollama

---------

Co-authored-by: Fernando Maclen <[email protected]>

fix: auto-scroll after submitting prompt (#155)

Closes #135

fix: minor adjustments to dark mode and mobile layouts

fix: remove "balance" text-wrapping

The shifting text while a completion is in progress is too distracting

feat: add "Message of the day" (#152)

Closes #50