Add Send to channel for thread messages (#5305)

## Summary

- Share eligible self-authored or owned-agent thread messages into the
parent channel as new top-level messages.
- Link the shared message back to the exact root thread with a semantic
channel label and excerpt.
- Add a dedicated channel-arrow icon plus ownership and navigation
coverage.

## Validation

- Desktop lint, size, and text guards
- Desktop TypeScript build and all 4,543 unit tests
- Focused Playwright send-to-channel and thread-link navigation tests

---------

Signed-off-by: kenny lopez <klopez4212@gmail.com>
Signed-off-by: Kenny Lopez <klopez4212@gmail.com>
Signed-off-by: Wes <wesbillman@users.noreply.github.com>
Co-authored-by: Carl <3c4caeafb646d23867f1c4832e68211d77e2561946171625f75c3ce1a3f2670f@buzz.block.builderlab.xyz>
Co-authored-by: Princess Donut <b238ea756dee4d98afa5883fc7f1de61eeabe65bf700e3a5a5a80db5e42e2c2b@buzz.block.builderlab.xyz>
Co-authored-by: Fast Fizz <2df81cb51f05a9d5387ef24d7b9ecb8fcdfcd1c70ffabc67061c9596e1b5b1c4@buzz.block.builderlab.xyz>
Co-authored-by: Wes <wesbillman@users.noreply.github.com>
Co-authored-by: Carl <c7ebe626f000404285d3686e1dc74cc07cc60a9754a150041ba132e14bd3e2ec@buzz.block.builderlab.xyz>

desktop/src/shared/api/editMessage.ts

@@ -8,6 +8,7 @@ export async function editMessage(
   emojiTags?: string[][],
   mentionPubkeys?: string[],
   suppressLinkPreviews?: boolean,
+  mentionTags?: string[][],
 ): Promise<void> {
   await invokeTauri("edit_message", {
     input: {
@@ -18,6 +19,7 @@ export async function editMessage(
       emojiTags: emojiTags ?? [],
       mentionPubkeys: mentionPubkeys ?? [],
       suppressLinkPreviews: suppressLinkPreviews ?? false,
+      mentionTags: mentionTags ?? null,
     },
   });
 }