fix(build): keep scripts/build/inputs.py free of pm imports; accept musl targets in its grammar

The Nix agent derivation builds scripts/build/*.py from a fileset that
does not include pm/, so importing pm.store.ALL_TARGETS there failed
nix flake check with ModuleNotFoundError. Extend the local target
regex with linux-(x64|arm64)-musl instead.

scripts/build/inputs.py

@@ -7,8 +7,6 @@ import json
 import re
 import tomllib
 
-from pm.store import ALL_TARGETS
-
 
 RESOURCE_ENV = {
     "skills": "HERMES_BUNDLED_SKILLS",
@@ -72,7 +70,7 @@ class AgentInputs:
         return cls(**values)
 
     def validate(self, out: Path) -> None:
-        if self.target not in ALL_TARGETS:
+        if not re.fullmatch(r"(?:(?:linux|darwin|win32)-(?:x64|arm64)|linux-(?:x64|arm64)-musl|linux-arm64-bionic)", self.target):
             raise ValueError(f"unsupported target: {self.target}")
         if self.placement not in ("contained", "fixed", "references"):
             raise ValueError(f"unknown placement: {self.placement}")