Add PAC copilot error triage guidance to the Manage agent

[xenophobentx]

With pac 2.12.2 (current on NuGet), several pac copilot failures only print "Sorry, the app encountered a non-recoverable error" plus an exception type. The actual reason is in pac-log.txt under the pac tool folder (on macOS ~/.dotnet/tools/.store/microsoft.powerapps.cli.tool/<version>/.../logs/pac-log.txt). The Manage agent doesn't know about this, so it can only guess.

Examples I reproduced on a throwaway agent:

• pac copilot publish exits with code 1 and System.ArgumentException, yet the publish goes through. On one agent the exception was logged at 19:01:16 and the bot's publishedon, which was empty before, was set to 19:01:45. On another, four calls in a row all crashed, and publishedon still moved from 16:47:56 to 16:49:55 during them. This is the pac bug in PAC CLI: copilot publish fails on first attempt with "Invalid response format" due to race condition powerplatform-build-tools#1307.
• pac copilot push failing with YamlDotNet.Core.SemanticErrorException: the console doesn't name the file, and the log only gives line and column. In my case it was an unquoted ": " in workflows/<Name>-<id>/metadata.yml.
• pac copilot push failing on a WorkflowTool whose workflowId doesn't exist: the reason (Entity 'Workflow' With Id = ... Does Not Exist) is only in the log.

Proposal: a short error triage section in agents/copilot-studio-manage.md:

1. On a pac crash, show the exception type and tell the user where pac-log.txt is; if the user agrees, read the last FTL entry.
2. On a publish ArgumentException, report the CLI failure, then check whether the bot's publishedon moved past its previous value before saying whether the publish completed.
3. After a publish, expect pac copilot push to report "Remote changes conflict" (publishing writes publishedOn), and pull before pushing.

I can open a PR for this.