fix(windows): sweep remaining bare read_text/write_text sites + linter rule

AST-driven pass over every Path.read_text()/write_text() without an
explicit encoding= across non-test code: 71 sites in 34 files
(skills_hub, hermes_cli/main+profiles+service_manager+container_boot,
mem0/hindsight/honcho plugins, achievements dashboard, release/CI
scripts, productivity+comfyui skill helpers, agent/*). Verified zero
positional-encoding collisions before insertion; per-file compile()
check after.

Adds a check-windows-footguns rule flagging bare single-line
read_text/write_text (multi-line forms stay covered by the AST guard
test from #38985). Together with the salvaged contributor commits this
retires the ~169-site bare file-I/O class (#37423's long tail).

scripts/lint_diff.py

@@ -30,7 +30,7 @@ def _load_json(path: Path | None) -> list[dict]:
     if path is None or not path.exists() or path.stat().st_size == 0:
         return []
     try:
-        data = json.loads(path.read_text())
+        data = json.loads(path.read_text(encoding="utf-8"))
     except json.JSONDecodeError as exc:
         print(f"warning: could not parse {path}: {exc}", file=sys.stderr)
         return []
@@ -197,7 +197,7 @@ def main() -> int:
 
     summary = "\n".join(buf)
     if args.output:
-        args.output.write_text(summary)
+        args.output.write_text(summary, encoding="utf-8")
     else:
         print(summary)
     return 0