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/components/Node.vue

@@ -906,9 +906,6 @@ export default defineComponent({
 		--node-width: 75px;
 		--node-height: 75px;
 
-		& [class*='node-wrapper--connection-type'] {
-			--configurable-node-options: -10px;
-		}
 		.node-default {
 			.node-options {
 				background: color-mix(in srgb, var(--color-canvas-background) 80%, transparent);
@@ -976,7 +973,6 @@ export default defineComponent({
 		);
 		--configurable-node-icon-offset: 40px;
 		--configurable-node-icon-size: 30px;
-		--configurable-node-options: -10px;
 
 		.node-description {
 			top: calc(50%);
@@ -1004,7 +1000,7 @@ export default defineComponent({
 			}
 
 			.node-options {
-				left: var(--configurable-node-options, 65px);
+				left: 0;
 				height: 25px;
 			}
 
@@ -1053,12 +1049,6 @@ export default defineComponent({
 	.node-wrapper--config & {
 		--node--selected--box-shadow-radius: 4px;
 		border-radius: 60px;
-		background-color: hsla(
-			var(--color-foreground-base-h),
-			60%,
-			var(--color-foreground-base-l),
-			80%
-		);
 	}
 }
 
@@ -1442,7 +1432,7 @@ export default defineComponent({
 
 	// Some nodes allow for dynamic connection labels
 	// so we need to make sure the label does not overflow
-	&[data-endpoint-label-length='medium'] {
+	&.node-connection-type-main[data-endpoint-label-length='medium'] {
 		max-width: calc(var(--stalk-size) - (var(--endpoint-size-small)));
 		overflow: hidden;
 		text-overflow: ellipsis;