chore: delete 106 unreachable *_system.gd and their parity tests

These files were loaded only by their own test_*_parity.gd and never by
the runtime (transitively checked, incl. client_phase_integration_system).
Removes 76 manifest implementation/evidence references across 18
contracts; contract docs get a note that conclusions based on them are
void. Live systems kept: chest, consumable, item_attr, metin_socket,
whisper_chat.

Full headless suite: no new failures (7 failing + 5 headless-hanging
render tests are identical before the deletion).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

audit/reports/coverage.md

@@ -24,10 +24,10 @@ Total contracts: 45
 
 ## Pending branch items
 
-- Total: 224
-- P0: 93
-- P1: 118
-- P2: 13
+- Total: 241
+- P0: 94
+- P1: 132
+- P2: 15
 - P3: 0
 - Routing: see `audit/remediation-roadmap.md`