core: drop two manifest fields that were never wired up

`SystemdSpec.readiness` (ReadinessHttpGet) and `SystemdSpec.requires` were
parsed and validated but read nowhere — no generator, CLI or API touched
either. Both looked load-bearing and were not:

- readiness duplicated `expose.http.health_path`, which wildpc-api already
  polls. wild-life-api.yaml declared both spellings of the same /health
  probe; only one did anything.
- requires would mean systemd `Requires=`, a lifecycle binding (stop
  postgres, stop every dependent). `manage.systemd.after` already gives the
  ordering callers actually want, and a deployment's own `requires:` is the
  relationship model, not systemd wiring.

Unknown keys parse as ignored, so existing deployment YAML keeps loading.

core/src/wildpc_core/manifest.py

@@ -142,19 +142,16 @@ LaunchSpec = Annotated[
 # ---------------------
 
 
-class ReadinessHttpGet(BaseModel):
-    http_get: str
-    timeout_seconds: int = 2
-    interval_seconds: int = 2
-    success_codes: list[int] = Field(default_factory=lambda: [200])
-
-
 class SystemdSpec(BaseModel):
     enable: bool = True
     user: bool = True
     description: str | None = None
+    # Unit ordering (systemd ``After=``). There is deliberately no ``requires:``
+    # partner emitting ``Requires=``: that binds lifecycles, so stopping postgres
+    # would stop everything downstream, and ordering is what callers actually
+    # want. A deployment's own ``requires:`` list is the relationship model (see
+    # docs/relationships.md), not systemd wiring.
     after: list[str] = Field(default_factory=list)
-    requires: list[str] = Field(default_factory=list)
     wanted_by: list[str] = Field(default_factory=lambda: ["default.target"])
     restart: RestartPolicy = RestartPolicy.ON_FAILURE
     restart_sec: int = 2
@@ -172,7 +169,6 @@ class SystemdSpec(BaseModel):
     start_limit_burst: int = 10
     start_limit_interval_sec: int = 3600
     no_new_privileges: bool = True
-    readiness: ReadinessHttpGet | None = None
     exec_reload: str | None = None
     # Commands run after the main process starts (systemd ``ExecStartPost=``), one
     # line each — e.g. an OpenBao auto-unseal step. Failures don't fail the unit.