conformance: fix startup-home tilde expansion

[ewhauser]

Summary

• make ordinary argv-style tilde expansion prefer the shell startup home while keeping redirect and parameter-expansion behavior intact
• use startup-home tilde semantics for compound-array keyed RHS values
• remove stale tilde-related xfails from the bash conformance manifest

Testing

• make lint
• go test ./shell/expand ./internal/shell/interp
• GBASH_CONFORMANCE_BASH=$(./scripts/ensure-bash.sh) GBASH_RUN_CONFORMANCE=1 go test ./internal/conformance -run 'TestConformance/bash/oils/(array-literal|array|brace-expansion|loop|word-split|tilde).test.sh$' -count=1

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[chatgpt-codex-connector]

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