fix(playback): freeze v3 seek reanchor recipes (#548)

* fix(playback): freeze v3 seek reanchor recipes

* fix(playback): address v3 recipe review feedback

* test(playback): isolate v3 fallback route fixture

* fix(database): split v3 recipe constraint validation

* fix(playback): preserve frozen seek recipe identity

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Co-authored-by: Quick104 <31828688+Quick104@users.noreply.github.com>

migrations/sql/20260806083316_add_playback_v3_frozen_recipe.sql

@@ -0,0 +1,12 @@
+-- +goose Up
+ALTER TABLE playback_v3_attempts
+    ADD COLUMN frozen_recipe JSONB NOT NULL DEFAULT '{}'::jsonb;
+
+ALTER TABLE playback_v3_attempts
+    ADD CONSTRAINT playback_v3_attempts_frozen_recipe_object
+        CHECK (jsonb_typeof(frozen_recipe) = 'object') NOT VALID;
+
+-- +goose Down
+ALTER TABLE playback_v3_attempts
+    DROP CONSTRAINT IF EXISTS playback_v3_attempts_frozen_recipe_object,
+    DROP COLUMN IF EXISTS frozen_recipe;

migrations/sql/20260806120421_validate_playback_v3_frozen_recipe.sql

@@ -0,0 +1,8 @@
+-- +goose Up
+ALTER TABLE playback_v3_attempts
+    VALIDATE CONSTRAINT playback_v3_attempts_frozen_recipe_object;
+
+-- +goose Down
+-- PostgreSQL cannot mark a validated CHECK constraint NOT VALID again. The
+-- preceding migration's Down step drops the constraint with its column.
+SELECT 1;