refactor(#1758): data-drive copyWithPathReplacement converter dispatch (#1759)

ADR-1239 Phase B (parent #1679). Replace copyWithPathReplacement's 13
hardcoded `const isX = runtime === 'x'` flags + two ~100-line per-runtime
if/else converter chains with a module-level RUNTIME_CONTENT_DISPATCH table
(one entry per runtime: md transform, mdSkipGenericRewrite, mdReattributeAfter,
mdTomlRenameOnCommand, js transform) + a uniform dispatch loop that applies the
cross-cutting steps (path rewrite -> attribution -> stamp -> normalize) once.

Byte-identical install output for all 16 runtimes (golden-parity harness #1730);
codex-verified the transform order + every per-runtime quirk (gemini .toml
rename, copilot/antigravity skip-generic + reattribute, qwen/hermes inline
swaps, .cjs/.js fall-through) is preserved.

Also folds in a pre-existing bookkeeping fix (no-defer): gsd-core/bin/lib/
cli-skew-check.cjs (tsc build artifact from #1755) was eslint-ignored but
missing from .gitignore — added for consistency with the other built artifacts.

Closes #1758

Co-authored-by: review-bot <review-bot@gsd>
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.changeset/eager-elks-frolic.md

@@ -0,0 +1,7 @@
+---
+type: Changed
+pr: 1759
+---
+**Internal: copyWithPathReplacement converter selection is now data-driven** — the installer's back-compat content-copy path replaced its 13 hardcoded `runtime === 'x'` flag chains with a single per-runtime dispatch table (ADR-1239 Phase B). Install output is byte-identical for all 16 runtimes (golden-parity asserted); no user-facing change.
+
+<!-- docs-exempt: internal refactor, no user-facing surface -->