feat: AI nodes usability fixes + Summarization Chain V2 (#7949)

Fixes:
- Refactor connection snapping when dragging and enable it also for
non-main connection types
- Fix propagation of errors from sub-nodes
- Fix chat scrolling when sending/receiving messages
- Prevent empty chat messages
- Fix sub-node selected styles
- Fix output names text overflow

Usability improvements:
- Auto-add manual chat trigger for agents & chain nodes
- Various labels and description updates
- Make the output parser input optional for Basic LLM Chain
- Summarization Chain V2 with a simplified document loader & text
chunking mode

#### How to test the change:
Example workflow showcasing different operation mode of the new
summarization chain:

[Summarization_V2.json](https://github.com/n8n-io/n8n/files/13599901/Summarization_V2.json)


## Issues fixed
Include links to Github issue or Community forum post or **Linear
ticket**:
> Important in order to close automatically and provide context to
reviewers
-
https://www.notion.so/n8n/David-Langchain-Posthog-notes-7a9294938420403095f4508f1a21d31d
- https://linear.app/n8n/issue/N8N-7070/ux-fixes-batch
- https://linear.app/n8n/issue/N8N-7071/ai-sub-node-bugs


## Review / Merge checklist
- [x] PR title and summary are descriptive. **Remember, the title
automatically goes into the changelog. Use `(no-changelog)` otherwise.**
([conventions](https://github.com/n8n-io/n8n/blob/master/.github/pull_request_title_conventions.md))
- [x] [Docs updated](https://github.com/n8n-io/n8n-docs) or follow-up
ticket created.
- [ ] Tests included.
> A bug is not considered fixed, unless a test is added to prevent it
from happening again. A feature is not complete without tests.
  >
> *(internal)* You can use Slack commands to trigger [e2e
tests](https://www.notion.so/n8n/How-to-use-Test-Instances-d65f49dfc51f441ea44367fb6f67eb0a?pvs=4#a39f9e5ba64a48b58a71d81c837e8227)
or [deploy test
instance](https://www.notion.so/n8n/How-to-use-Test-Instances-d65f49dfc51f441ea44367fb6f67eb0a?pvs=4#f6a177d32bde4b57ae2da0b8e454bfce)
or [deploy early access version on
Cloud](https://www.notion.so/n8n/Cloudbot-3dbe779836004972b7057bc989526998?pvs=4#fef2d36ab02247e1a0f65a74f6fb534e).

---------

Signed-off-by: Oleg Ivaniv <me@olegivaniv.com>
Co-authored-by: Elias Meire <elias@meire.dev>

packages/editor-ui/src/plugins/i18n/locales/en.json

@@ -140,6 +140,8 @@
 	"chat.window.noExecution": "Nothing got executed yet",
 	"chat.window.chat.placeholder": "Type in message",
 	"chat.window.chat.sendButtonText": "Send",
+	"chat.window.chat.provideMessage": "Please provide a message",
+	"chat.window.chat.emptyChatMessage": "Empty chat message",
 	"chat.window.chat.chatMessageOptions.reuseMessage": "Reuse Message",
 	"chat.window.chat.chatMessageOptions.repostMessage": "Repost Message",
 	"chat.window.chat.chatMessageOptions.executionId": "Execution ID",
@@ -925,6 +927,7 @@
 	"nodeCreator.aiPanel.aiOtherNodesDescription": "Embeddings, Vector Stores, LLMs and other AI nodes",
 	"nodeCreator.aiPanel.selectAiNode": "Select an Al Node to add to your workflow",
 	"nodeCreator.aiPanel.nodesForAi": "Build autonomous agents, summarize or interrogate documents, etc.",
+	"nodeCreator.aiPanel.newTag": "New",
 	"nodeCreator.aiPanel.langchainAiNodes": "Advanced AI",
 	"nodeCreator.aiPanel.title": "When should this workflow run?",
 	"nodeCreator.aiPanel.infoBox": "Check out our <a href=\"/collections/8\" target=\"_blank\">templates</a> for workflow examples and inspiration.",