fix(资源路径): 从 Host 项目根解析相对配置

将 .env 固定定位到 script_build_host 项目根，并对 agent-data、persona、section、decode、knowledge 和 prompt 等资源路径做项目根相对解析。代码从任意工作目录启动都读取同一套 legacy inputs。

script_build_host/src/script_build_host/infrastructure/config.py

@@ -22,11 +22,23 @@ from script_build_host.domain.task_contracts import (
     PhaseTwoLimits,
 )
 
+PROJECT_ROOT = Path(__file__).resolve().parents[3]
+_PROJECT_PATH_FIELDS = (
+    "agent_data_root",
+    "persona_root",
+    "section_pattern_root",
+    "decode_index_root",
+    "decode_raw_root",
+    "knowledge_root",
+    "prompt_fallback_root",
+)
+
 
 class ScriptBuildSettings(BaseSettings):
     model_config = SettingsConfigDict(
         env_prefix="SCRIPT_BUILD_",
-        env_file=".env",
+        env_file=PROJECT_ROOT / ".env",
+        env_file_encoding="utf-8",
         extra="ignore",
         case_sensitive=False,
         populate_by_name=True,
@@ -122,6 +134,16 @@ class ScriptBuildSettings(BaseSettings):
     )
     phase_two_max_repairs_per_trace: int = Field(default=1, ge=1, le=1)
 
+    @model_validator(mode="after")
+    def resolve_project_paths(self) -> Self:
+        """Resolve portable resource paths from the Script Build project root."""
+
+        for field_name in _PROJECT_PATH_FIELDS:
+            value = getattr(self, field_name)
+            if value is not None and not value.is_absolute():
+                setattr(self, field_name, (PROJECT_ROOT / value).resolve())
+        return self
+
     @model_validator(mode="after")
     def validate_database_separation(self) -> Self:
         read_url = make_url(self.read_database_url.get_secret_value())