Make Play Button stateful and remove intent toggle

[thenamankumar]

This PR:

• Removes the intent toggle feature completely.
• Changes the intent dropdown behavior to only select the intent and not execute it automatically.
• Enables the submit button even when the chat is empty.

Test plan

• the intent options in the dropdown only selects the intent mode and doesn't execute it.
• after selecting the intent, changing the input, doesn't reset the intent.
• on submit the selected intent is used and the intent selection message is displayed accordingly.
• loading a chat from history and editing the message, doesn't persist the intent mode previously manually selected.
• selecting a prompt correctly executes it in chat & edit modes.
• make sure the submit button isn't disabled when the input is empty.

[janhartman]

Code LGTM, but I'll defer to Erika/Beyang for the backport approval :)

[bahrmichael]

LGTM

[sourcegraph-release-bot]

The backport to vscode-v1.64.x failed at https://github.com/sourcegraph/cody/actions/runs/13007104159:

The process '/usr/bin/git' failed with exit code 1

To backport this PR manually, you can either:

Via the sg tool

Use the sg backport command to backport your commit to the release branch.

sg backport -r vscode-v1.64.x -p 6833

Via your terminal

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-vscode-v1.64.x vscode-v1.64.x
# Navigate to the new working tree
cd .worktrees/backport-vscode-v1.64.x
# Create a new branch
git switch --create backport-6833-to-vscode-v1.64.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 2edd2640026853acb0038300c60cb6b08fffc3a6
# Push it to GitHub
git push --set-upstream origin backport-6833-to-vscode-v1.64.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-vscode-v1.64.x

If you encouter conflict, first resolve the conflict and stage all files, then run the commands below:

git cherry-pick --continue
# Push it to GitHub
git push --set-upstream origin backport-6833-to-vscode-v1.64.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-vscode-v1.64.x

• Follow above instructions to backport the commit.
• Create a pull request where the base branch is vscode-v1.64.x and the compare/head branch is backport-6833-to-vscode-v1.64.x., click here to create the pull request.

Once the pull request has been created, please ensure the following:

• Make sure to tag @sourcegraph/release in the pull request description.

• kindly remove the release-blocker from this pull request.

[sourcegraph-release-bot]

The backport to jb-v7.12.x failed at https://github.com/sourcegraph/cody/actions/runs/13007104159:

The process '/usr/bin/git' failed with exit code 1

To backport this PR manually, you can either:

Via the sg tool

Use the sg backport command to backport your commit to the release branch.

sg backport -r jb-v7.12.x -p 6833

Via your terminal

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-jb-v7.12.x jb-v7.12.x
# Navigate to the new working tree
cd .worktrees/backport-jb-v7.12.x
# Create a new branch
git switch --create backport-6833-to-jb-v7.12.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 2edd2640026853acb0038300c60cb6b08fffc3a6
# Push it to GitHub
git push --set-upstream origin backport-6833-to-jb-v7.12.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-jb-v7.12.x

If you encouter conflict, first resolve the conflict and stage all files, then run the commands below:

git cherry-pick --continue
# Push it to GitHub
git push --set-upstream origin backport-6833-to-jb-v7.12.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-jb-v7.12.x

• Follow above instructions to backport the commit.
• Create a pull request where the base branch is jb-v7.12.x and the compare/head branch is backport-6833-to-jb-v7.12.x., click here to create the pull request.

Once the pull request has been created, please ensure the following:

• Make sure to tag @sourcegraph/release in the pull request description.

• kindly remove the release-blocker from this pull request.

[thenamankumar]

These changes are pre-approved by @beyang during Monday's team sync. Merging the backports to unblock.