* merge: rebase onto main, combine Windows shell guidance with #476's MSYS text
#476 merged into main and rewrote the same "Shell syntax: Windows cmd.exe..."
guidance string in system_prompt.go and shellGuidanceForGOOS in
shell_runtime.go that this branch also edits (this PR's fix for the broken
single-quoted quoting examples). Combined both into one coherent string in
each spot: the double-quote/single-quote metachar rule with correct
examples, plus #476's MSYS coreutils warning and require_escalated
mention. Merged the corresponding test assertions in loop_test.go the
same way.
internal/imageinput/clipboard.go, internal/tools/bash_tool_test.go, and
internal/tools/exec_command_test.go applied cleanly with no overlap.
* test(tools): add host shell syntax description test for exec_command
* chore: retrigger CI after infra flake
* style(tools): gofmt exec_command_test.go
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Co-authored-by: Vasanthdev2004 <[email protected]>