fix(#2352): expand tilde paths in review scope before the deleted-file filter (#2419)

* fix(#2352): tilde-expand SUMMARY.md key-files paths before deleted-file filter

compute_file_scope's "Filter deleted files" step tested the literal `~/...`
value from SUMMARY.md key-files entries with `[ -f "$file" ]`, which bash
never tilde-expands (only a literal `~` in source text expands, not one
arriving as an already-expanded variable value). Real files recorded with a
`~/...` path were silently misclassified as deleted and dropped from
REVIEW_FILES, and a phase whose every recorded file used a tilde path hit the
empty-scope skip as a false negative.

Adds a tilde-normalization loop as step 1 of post-processing (all tiers),
before the deleted-file filter, rewriting a leading `~/` to `${HOME}/...` so
downstream existence checks, the empty-scope short-circuit, and the
FILES_TO_READ/CONFIG_FILES construction all see a real, openable path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#2352): regenerate fixtures + lint gate-prep

* chore(#2352): add Fixed changeset fragment (pr 2419)

---------

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

tests/fixtures/golden-install-parity/codebuddy.json

@@ -288,7 +288,7 @@
   "gsd-core/workflows/check-todos.md": "bdeaf43f9c61e0cc",
   "gsd-core/workflows/cleanup.md": "0daa2f2720c111f1",
   "gsd-core/workflows/code-review-fix.md": "2e113d1f4350a075",
-  "gsd-core/workflows/code-review.md": "334c90c401f291f8",
+  "gsd-core/workflows/code-review.md": "2aa1957579f50a87",
   "gsd-core/workflows/complete-milestone.md": "c1f91b77f4ace7f2",
   "gsd-core/workflows/debug.md": "98c8ed5af882ef8f",
   "gsd-core/workflows/diagnose-issues.md": "77d98ac07c4a26ff",