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/fix_line_204.py

@@ -0,0 +1,28 @@
+"""Fix the contradictory line 204 in error_handling.md."""
+from __future__ import annotations
+
+import sys
+from pathlib import Path
+
+DOC = Path("conductor/code_styleguides/error_handling.md")
+
+OLD = "  grok); `send()` is the new public API; `send()` is `@deprecated`."
+
+NEW = "  grok); `send(...) -> Result[str, ErrorInfo]` is the public API."
+
+
+def main() -> int:
+ with DOC.open("r", encoding="utf-8", newline="") as f:
+  content = f.read()
+ if OLD not in content:
+  print(f"NOT FOUND: {OLD!r}", file=sys.stderr)
+  return 1
+ new_content = content.replace(OLD, NEW, 1)
+ with DOC.open("w", encoding="utf-8", newline="") as f:
+  f.write(new_content)
+ print("Line 204 fixed.")
+ return 0
+
+
+if __name__ == "__main__":
+ raise SystemExit(main())