Add set -o pipefail to all bin scripts

[remenoscodes]

The Quality Gates workflow enforces pipefail in all bin scripts, but adding it naively breaks pipes that use | head due to SIGPIPE (exit 141).

Requires a careful refactor:

1. Switch shebang from #\!/bin/sh to #\!/usr/bin/env bash (pipefail is not POSIX)
2. Add set -o pipefail after set -e in all 20 executable scripts
3. Handle SIGPIPE in all | head, | sed ... | head, and similar truncating pipelines
4. Options: trap '' PIPE, || true on specific pipes, or restructure to avoid early-exit readers

Affected pipelines (examples):

• git log ... | sed | head -1 in git-issue-show (state extraction)
• git for-each-ref ... | awk | sort in git-issue-ls
• Similar patterns in most bin scripts (6,301 total lines, 400+ pipe usages)

Attempted quick fix (shebang + pipefail) caused exit 141 across core tests. Reverted.

[remenoscodes]

Closing as won't fix. After multiple attempts (including a prior revert and PR #152's thorough SIGPIPE remediation), the cost/benefit doesn't justify the change:

• Adding set -o pipefail requires switching from #!/bin/sh to #!/bin/bash, breaking POSIX compatibility — a core project constraint
• The codebase is 100% POSIX-clean today, matching Git's own CodingGuidelines convention
• 33 pipefail exemption wrappers would be needed (11 unnecessary, 8 eliminable with better patterns)
• A regression in git-issue-lib's get_issue_title() was identified during review

The valuable part — git log -1 optimizations that eliminate pipes entirely — can land as a separate, POSIX-safe improvement.