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.

gateway/platforms/telegram.py

@@ -744,7 +744,7 @@ class TelegramAdapter(BasePlatformAdapter):
                 return
 
             import yaml as _yaml
-            with open(config_path, "r") as f:
+            with open(config_path, "r", encoding="utf-8") as f:
                 config = _yaml.safe_load(f) or {}
 
             # Navigate to platforms.telegram.extra.dm_topics
@@ -3516,7 +3516,7 @@ class TelegramAdapter(BasePlatformAdapter):
                 return
 
             import yaml as _yaml
-            with open(config_path, "r") as f:
+            with open(config_path, "r", encoding="utf-8") as f:
                 config = _yaml.safe_load(f) or {}
 
             dm_topics = (

gateway/platforms/whatsapp.py

@@ -526,7 +526,7 @@ class WhatsAppAdapter(BasePlatformAdapter):
             # messages are preserved for troubleshooting.
             whatsapp_mode = os.getenv("WHATSAPP_MODE", "self-chat")
             self._bridge_log = self._session_path.parent / "bridge.log"
-            bridge_log_fh = open(self._bridge_log, "a")
+            bridge_log_fh = open(self._bridge_log, "a", encoding="utf-8")
             self._bridge_log_fh = bridge_log_fh
 
             # Build bridge subprocess environment.
@@ -1170,7 +1170,7 @@ class WhatsAppAdapter(BasePlatformAdapter):
                             if file_size > MAX_TEXT_INJECT_BYTES:
                                 print(f"[{self.name}] Skipping text injection for {doc_path} ({file_size} bytes > {MAX_TEXT_INJECT_BYTES})", flush=True)
                                 continue
-                            content = Path(doc_path).read_text(errors="replace")
+                            content = Path(doc_path).read_text(encoding="utf-8", errors="replace")
                             fname = Path(doc_path).name
                             # Remove the doc_<hex>_ prefix for display
                             display_name = fname

gateway/status.py

@@ -113,7 +113,7 @@ def _get_process_start_time(pid: int) -> Optional[int]:
     stat_path = Path(f"/proc/{pid}/stat")
     try:
         # Field 22 in /proc/<pid>/stat is process start time (clock ticks).
-        return int(stat_path.read_text().split()[21])
+        return int(stat_path.read_text(encoding="utf-8").split()[21])
     except (FileNotFoundError, IndexError, PermissionError, ValueError, OSError):
         return None
 
@@ -197,7 +197,7 @@ def _read_json_file(path: Path) -> Optional[dict[str, Any]]:
     if not path.exists():
         return None
     try:
-        raw = path.read_text().strip()
+        raw = path.read_text(encoding="utf-8").strip()
     except OSError:
         return None
     if not raw:
@@ -523,7 +523,7 @@ def acquire_scoped_lock(scope: str, identity: str, metadata: Optional[dict[str,
                     try:
                         _proc_status = Path(f"/proc/{existing_pid}/status")
                         if _proc_status.exists():
-                            for _line in _proc_status.read_text().splitlines():
+                            for _line in _proc_status.read_text(encoding="utf-8").splitlines():
                                 if _line.startswith("State:"):
                                     _state = _line.split()[1]
                                     if _state in ("T", "t"):  # stopped or tracing stop