feat(helpers4-common): warn about unfixable host-bound git config paths

[baxyz]

Summary

• git-config-self-heal.sh only ever fixed shell-out keys (PATH-searchable) and an SSH signing key (derivable from the forwarded agent). core.hooksPath, core.excludesfile, core.attributesfile, and include.path/includeIf.*.path all point at a file or directory that only ever existed on the host, with no equivalent recovery path — adds a warning-only check for all four, matching the script's existing best-effort/never-fails contract.
• git config --file never follows includes, so an included file's own contents (if it even exists) stay invisible to every check in this script — this can only confirm whether the included file itself is present. Documented in both the script and the README.
• Also fixes the shell-out key list in the README, which still said "core.editor" without core.sshCommand (added in a prior release and never backfilled there).
• Patch bump (1.2.0 → 1.2.1), not minor: this only adds diagnostic warnings for paths self-heal already couldn't do anything about — nothing it fixes or enables changed.

Verified end-to-end, not just unit-style: installed the real generated common.sh and git-config-self-heal.sh at their actual /usr/local/share/helpers4/ path and ran the full test/helpers4-common/test.sh against them. Caught and fixed a real bug this way — git normalizes includeIf's key to lowercase (includeif, not includeIf), so the first version of that check never matched anything.

Board card: "Self-heal: warn on host-bound config paths that can't be repaired (hooksPath, excludesfile, includeIf)" (Backlog, Low priority).

Test plan

• bash -n syntax check, JSON validated
• Full end-to-end run against the real installed files: missing hooksPath/excludesfile/include.path/includeIf.*.path each warn without failing, an existing path is left alone, no keys set = silent no-op
• New test cases added to test/helpers4-common/test.sh
• CI

🤖 Generated with Claude Code

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📋 Pipeline Status

	Job	Status
✅	🧾 Conventional Commits	passing
✅	🔖 Version Bump	passing
✅	🧪 Feature Tests	passing
✅	🐚 ShellCheck	passing

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_{🤖 Generated by @helpers4 CI • 2026-09-08}