codebase: add encoding='utf-8' to all bare open() calls (PLW1514)

Closes the last Python-on-Windows UTF-8 exposure by making every
text-mode open() call explicit about its encoding.

Before: on Windows, bare open(path, 'r') defaults to the system
locale encoding (cp1252 on US-locale installs).  That means reading
any config/yaml/markdown/json file with non-ASCII content either
crashes with UnicodeDecodeError or silently mis-decodes bytes.

After: all 89 affected call sites in production code now pass
encoding='utf-8' explicitly.  Works identically on every platform
and every locale, no surprise behavior.

Mechanical sweep via:
  ruff check --preview --extend-select PLW1514 --unsafe-fixes --fix     --exclude 'tests,venv,.venv,node_modules,website,optional-skills,               skills,tinker-atropos,plugins' .

All 89 fixes have the same shape: open(x) or open(x, mode) became
open(x, encoding='utf-8') or open(x, mode, encoding='utf-8').  Nothing
else changed.  Every modified file still parses and the Windows/sandbox
test suite is still green (85 passed, 14 skipped, 0 failed across
tests/tools/test_code_execution_windows_env.py +
tests/tools/test_code_execution_modes.py + tests/tools/test_env_passthrough.py +
tests/test_hermes_bootstrap.py).

Scope notes:
  - tests/ excluded: test fixtures can use locale encoding intentionally
    (exercising edge cases).  If we want to tighten tests later that's
    a separate PR.
  - plugins/ excluded: plugin-specific conventions may differ; plugin
    authors own their code.
  - optional-skills/ and skills/ excluded: skill scripts are user-authored
    and we don't want to mass-edit them.
  - website/ and tinker-atropos/ excluded: vendored / generated content.

46 files touched, 89 +/- lines (symmetric replacement).  No behavior
change on POSIX or on Windows when the file is ASCII; bug fix on
Windows when the file contains non-ASCII.

scripts/build_model_catalog.py

@@ -81,7 +81,7 @@ def build_catalog() -> dict:
 def main() -> int:
     catalog = build_catalog()
     os.makedirs(os.path.dirname(OUTPUT_PATH), exist_ok=True)
-    with open(OUTPUT_PATH, "w") as fh:
+    with open(OUTPUT_PATH, "w", encoding="utf-8") as fh:
         json.dump(catalog, fh, indent=2)
         fh.write("\n")
 

scripts/build_skills_index.py

@@ -304,7 +304,7 @@ def main():
     }
 
     os.makedirs(os.path.dirname(OUTPUT_PATH), exist_ok=True)
-    with open(OUTPUT_PATH, "w") as f:
+    with open(OUTPUT_PATH, "w", encoding="utf-8") as f:
         json.dump(index, f, separators=(",", ":"), ensure_ascii=False)
 
     elapsed = time.time() - overall_start

scripts/contributor_audit.py

@@ -291,7 +291,7 @@ def check_release_file(release_file, all_contributors):
         missing: set of handles NOT found in the file
     """
     try:
-        content = Path(release_file).read_text()
+        content = Path(release_file).read_text(encoding="utf-8")
     except FileNotFoundError:
         print(f"  [error] Release file not found: {release_file}", file=sys.stderr)
         return set(), set(all_contributors)

scripts/discord-voice-doctor.py

@@ -242,7 +242,7 @@ def check_config(groq_key, eleven_key):
     if config_path.exists():
         try:
             import yaml
-            with open(config_path) as f:
+            with open(config_path, encoding="utf-8") as f:
                 cfg = yaml.safe_load(f) or {}
 
             stt_provider = cfg.get("stt", {}).get("provider", "local")

scripts/profile-tui.py

@@ -111,7 +111,7 @@ def summarize(log: Path, since_ts_ms: int) -> dict[str, Any]:
     frame_events: list[dict[str, Any]] = []
     if not log.exists():
         return {"error": f"no log at {log}", "react": [], "frame": []}
-    for line in log.read_text().splitlines():
+    for line in log.read_text(encoding="utf-8").splitlines():
         line = line.strip()
         if not line:
             continue
@@ -505,7 +505,7 @@ def main() -> int:
 
     if args.save:
         path = Path(f"/tmp/perf-{args.save}.json")
-        path.write_text(json.dumps(metrics, indent=2))
+        path.write_text(json.dumps(metrics, indent=2), encoding="utf-8")
         print(f"\n• saved: {path}")
 
     if args.compare:

scripts/release.py

@@ -1365,7 +1365,7 @@ def main():
     )
 
     if args.output:
-        Path(args.output).write_text(changelog)
+        Path(args.output).write_text(changelog, encoding="utf-8")
         print(f"Changelog written to {args.output}")
     else:
         print(changelog)