fix(packaging): ship bundled skills in wheel

Salvages #23738 by @LeonSGP43. Wheel installs were missing skills/ and
optional-skills/ because pyproject's [tool.setuptools.packages.find]
only includes Python packages — the skills directories don't have
__init__.py so they were silently dropped from the wheel.

Adds setup.py with data_files spec emitting skills/* and optional-skills/*
under hermes_agent-<v>.data/data/, and a get_bundled_skills_dir() helper
in hermes_constants that discovers the wheel-installed location via
sysconfig before falling back to a source-checkout path. tools/skills_sync
uses the helper so 'hermes update' works for pip-installed users.

hermes_constants.py

@@ -5,6 +5,7 @@ without risk of circular imports.
 """
 
 import os
+import sysconfig
 from contextvars import ContextVar, Token
 from pathlib import Path
 
@@ -139,6 +140,23 @@ def get_default_hermes_root() -> Path:
     return env_path
 
 
+def _get_packaged_data_dir(name: str) -> Path | None:
+    """Return an installed data-files directory if one exists.
+
+    Used to discover bundled skills/optional-skills when Hermes is installed
+    from a wheel that emitted them via setuptools data_files.
+    """
+    candidates = []
+    for scheme in ("data", "purelib", "platlib"):
+        raw = sysconfig.get_path(scheme)
+        if raw:
+            candidates.append(Path(raw) / name)
+    for candidate in candidates:
+        if candidate.exists():
+            return candidate
+    return None
+
+
 def get_optional_skills_dir(default: Path | None = None) -> Path:
     """Return the optional-skills directory, honoring package-manager wrappers.
 
@@ -148,11 +166,34 @@ def get_optional_skills_dir(default: Path | None = None) -> Path:
     override = os.getenv("HERMES_OPTIONAL_SKILLS", "").strip()
     if override:
         return Path(override)
+    packaged = _get_packaged_data_dir("optional-skills")
+    if packaged is not None:
+        return packaged
     if default is not None:
         return default
     return get_hermes_home() / "optional-skills"
 
 
+def get_bundled_skills_dir(default: Path | None = None) -> Path:
+    """Return the bundled skills directory for source and packaged installs.
+
+    Resolution order:
+        1. ``HERMES_BUNDLED_SKILLS`` env var (Nix wrapper / explicit override)
+        2. Wheel-installed ``<sysconfig data>/skills`` (pip install path)
+        3. Caller-supplied ``default`` (typically the source-checkout path)
+        4. ``<HERMES_HOME>/skills`` last-resort
+    """
+    override = os.getenv("HERMES_BUNDLED_SKILLS", "").strip()
+    if override:
+        return Path(override)
+    packaged = _get_packaged_data_dir("skills")
+    if packaged is not None:
+        return packaged
+    if default is not None:
+        return default
+    return get_hermes_home() / "skills"
+
+
 def get_hermes_dir(new_subpath: str, old_name: str) -> Path:
     """Resolve a Hermes subdirectory with backward compatibility.