Initial work on Vision support in text conversations and Image Editing

This is a huge patch which does some major refactoring like:

- renaming "Image Generation" to "Image Creation" in most places,
  to better match its new command (`!bai image create`)

- relocating image creation command (`!bai image` -> `!bai image create`),
  so it wouldn't conflict with the new image editing command (`!bai image edit`)

- introducing a new image editing command (`!bai image edit`), which
  is meant to work only with the OpenAI provider, but doesn't fully work yet
  due to https://github.com/64bit/async-openai/issues/364, though a next patch will fix it

- adding support for reading images off of Matrix conversations and forwarding them to
  text conversations. Works for OpenAI, but not for Anthropic yet
  (requires custom patches) and not for OpenAI-Compat (no support for
  images there)

- relocating some utils around (base64, mime)

src/controller/image/edit.rs

@@ -0,0 +1,163 @@
+use mxlink::{MatrixLink, MessageResponseType};
+
+use tracing::Instrument;
+
+use crate::agent::provider::ImageSource;
+use crate::agent::AgentPurpose;
+use crate::agent::ControllerTrait;
+use crate::agent::provider::ImageEditParams;
+use crate::controller::utils::agent::get_effective_agent_for_purpose_or_complain;
+use crate::utils::mime::get_file_extension;
+use crate::conversation::create_llm_conversation_for_matrix_thread;
+use crate::conversation::matrix::MatrixMessageProcessingParams;
+use crate::strings;
+use crate::{Bot, entity::MessageContext};
+
+pub async fn handle(
+    bot: &Bot,
+    matrix_link: MatrixLink,
+    message_context: &MessageContext,
+    original_prompt: &str,
+) -> anyhow::Result<()> {
+    let response_type = MessageResponseType::InThread(message_context.thread_info().clone());
+
+    let Some(agent) = get_effective_agent_for_purpose_or_complain(
+        bot,
+        message_context,
+        AgentPurpose::ImageGeneration,
+        response_type.clone(),
+        true,
+    )
+    .await
+    else {
+        return Ok(());
+    };
+
+    if message_context.thread_info().is_thread_root_only() {
+        return send_guide(bot, message_context).await;
+    }
+
+    let _typing_notice_guard = bot.start_typing_notice(message_context.room()).await;
+
+    let params = MatrixMessageProcessingParams::new(
+        bot.user_id().to_owned(),
+        Some(message_context.combined_admin_and_user_regexes()),
+    );
+
+    let conversation = create_llm_conversation_for_matrix_thread(
+        &matrix_link,
+        message_context.room(),
+        message_context.thread_info().root_event_id.clone(),
+        &params,
+    )
+    .await?;
+
+    let prompt = if conversation.messages.len() >= 2 {
+        // Skip the first message, which contains the original prompt (which we already have)
+        let other_messages = conversation.messages.iter().skip(1).cloned().collect();
+
+        super::prompt::build(original_prompt, other_messages)
+    } else {
+        original_prompt.to_owned()
+    };
+
+    let got_go_signal = conversation.messages.iter().any(|message| {
+        if let crate::conversation::llm::MessageContent::Text(text) = &message.content {
+            text.to_lowercase() == "go"
+        } else {
+            false
+        }
+    });
+
+    let image_sources: Vec<ImageSource> = conversation.messages.iter().filter_map(|message| {
+        if let crate::conversation::llm::MessageContent::Image(image_content) = &message.content {
+            Some(image_content.into())
+        } else {
+            None
+        }
+    }).collect();
+
+    if !got_go_signal || image_sources.is_empty() {
+        // We don't send the guide again here to avoid being annoying.
+        return Ok(());
+    }
+
+    let span = tracing::debug_span!(
+        "image_edit",
+        agent_id = agent.identifier().as_string()
+    );
+
+    let result = agent
+        .controller()
+        .create_image_edit(&prompt, image_sources, ImageEditParams::default())
+        .instrument(span)
+        .await;
+
+    let response = match result {
+        Ok(response) => response,
+        Err(err) => {
+            tracing::warn!(
+                "Error in room {} while trying to generate image edit via agent {}: {:?}",
+                message_context.room_id(),
+                agent.identifier(),
+                err,
+            );
+
+            bot.messaging()
+                .send_error_markdown_no_fail(
+                    message_context.room(),
+                    &strings::agent::error_while_serving_purpose(
+                        agent.identifier(),
+                        &AgentPurpose::ImageGeneration,
+                        &err,
+                    ),
+                    response_type,
+                )
+                .await;
+
+            return Ok(());
+        }
+    };
+
+    let attachment_body_text = format!(
+        "generated-image-edit.{}",
+        get_file_extension(&response.mime_type)
+    );
+
+    let mut event_content = matrix_link
+        .media()
+        .upload_and_prepare_event_content(
+            message_context.room(),
+            &response.mime_type,
+            response.bytes,
+            &attachment_body_text,
+        )
+        .await
+        .map_err(|e| anyhow::anyhow!("Failed to upload and prepare event: {}", e))?;
+
+    matrix_link
+        .messaging()
+        .send_event(
+            message_context.room(),
+            &mut event_content,
+            response_type.clone(),
+        )
+        .await?;
+
+    Ok(())
+}
+
+async fn send_guide(
+    bot: &Bot,
+    message_context: &MessageContext,
+) -> anyhow::Result<()> {
+    bot.messaging()
+        .send_text_markdown_no_fail(
+            message_context.room(),
+            strings::image_edit::guide_how_to_proceed(),
+            MessageResponseType::InThread(message_context.thread_info().clone()),
+        )
+        .await;
+
+    Ok(())
+}