docs(ai_client): rename send_result to send in 3 current docs

Doc consistency: guide_ai_client.md, guide_app_controller.md, and
the error_handling styleguide now reference the new symbol name.

Also fixes two consistency issues in error_handling.md introduced by
the mechanical rename:
1. The 'Deprecation: send -> send_result' section (lines 623-642) was
   rewritten as a 'Historical deprecation (added 2026-06-15, reverted
   2026-06-16)' note that points to the relevant track specs.
2. Line 204 (the 'Current State Audit' summary for src/ai_client.py)
   had a self-contradictory claim ('send() is the new public API;
   send() is @deprecated') after the rename. Updated to describe
   the canonical public API.

Historical archives (conductor/tracks/*/spec.md, conductor/tracks/*/plan.md,
docs/reports/*) are NOT modified - they document the 2026-06-15
public_api_migration decision and stay as historical record.

scripts/tier2/apply_t5_1_edits.py

@@ -0,0 +1,32 @@
+"""Apply Phase 5 mechanical rename to the 3 current docs."""
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+FILES = [
+ "docs/guide_ai_client.md",
+ "docs/guide_app_controller.md",
+ "conductor/code_styleguides/error_handling.md",
+]
+
+
+def main() -> int:
+ total = 0
+ for rel in FILES:
+  p = Path(rel)
+  with p.open("r", encoding="utf-8", newline="") as f:
+   content = f.read()
+  before = content.count("send_result")
+  new_content = content.replace("send_result", "send")
+  with p.open("w", encoding="utf-8", newline="") as f:
+   f.write(new_content)
+  remaining = new_content.count("send_result")
+  print(f"{rel}: {before} -> {before - remaining} (remaining={remaining})")
+  total += before - remaining
+ print(f"Total: {total} renamed")
+ return 0
+
+
+if __name__ == "__main__":
+ raise SystemExit(main())