Fix case-only source path aliases on macOS - #2372

Graphify reviewed this change.

Looks safe to merge — no coupling regressions and no blocking issues, checked against the code graph (not a self-assessment).

Graphify review — findings

This PR adds case-insensitive path alias handling to the graph reconciliation logic in graphify/watch.py. When a stored node's source path differs only by letter case from a currently scanned file, the code now attempts to confirm they point to the same on-disk file via os.path.samefile(), and if so treats the stored path as current rather than excluded—rebasing it to the scanner's canonical spelling. It also extends rebase_preserved to accept a mapping of canonical identities and builds a casefold lookup that discards ambiguous case-only collisions. On the test side, it adds test_reconcile_case_alias_uses_current_source_spelling, which monkeypatches samefile to simulate APFS case-insensitive behavior on case-sensitive CI and asserts the preserved node adopts the scanner's spelling without a fail-closed warning. The large set of renamed rationale_* test symbols appears to reflect surrounding test-file churn rather than substantive logic changes.

No blocking issues surfaced. 2 lower-confidence candidates did not survive cross-model review.