add: SVT-AV1 lp (thread cap) config knob

Add encoding.lp (0 = auto) so a long encode can be capped to N logical
processors instead of pinning every core, as a lighter-weight alternative to
the compose cgroup limit. Threaded config -> types.Job -> -svtav1-params via a
testable svtav1Params helper. Settings-UI surfacing stays with #1.

refs #5

pkg/types/types.go

@@ -16,6 +16,7 @@ type Job struct {
 	Metadata     *Metadata
 	CRF          int
 	Preset       int
+	LP           int // SVT-AV1 logical processors; 0 = auto
 	DeleteOrigin bool
 }
 
@@ -46,6 +47,9 @@ type EncodingConfig struct {
 	Bluray EncodingParams `yaml:"bluray"`
 	WebDL  EncodingParams `yaml:"webdl"`
 	TVRip  EncodingParams `yaml:"tvrip"`
+	// LP caps SVT-AV1's logical-processor (thread) count so a long encode can't
+	// pin every core. 0 = let SVT-AV1 auto-detect (default). Applies to all profiles.
+	LP int `yaml:"lp"`
 }
 
 type EncodingParams struct {