refactor(store,tools): migrate IDs from UUID to bigserial int64

All internal entity lookups now use bigserial primary keys (int64) while
GUIDs are retained for external/public identification. Updated store
functions (TouchProject, UpdateThoughtMetadata, AddThoughtAttachment) to
query by id instead of guid, added GetThoughtByID, changed semanticSearch
and all tool helpers to use *int64 project IDs, and updated retry/backfill
workers to use int64 thought IDs throughout.

internal/tools/learnings_test.go

@@ -5,7 +5,6 @@ import (
 	"testing"
 
 	"git.warky.dev/wdevs/amcs/internal/mcperrors"
-	"github.com/google/uuid"
 )
 
 func TestLearningsAddRequiresSummary(t *testing.T) {
@@ -37,7 +36,7 @@ func TestLearningsMethodsRequireConfiguredStore(t *testing.T) {
 	})
 
 	t.Run("get", func(t *testing.T) {
-		_, _, err := tool.Get(context.Background(), nil, GetLearningInput{ID: uuid.New()})
+		_, _, err := tool.Get(context.Background(), nil, GetLearningInput{ID: 0})
 		if err == nil {
 			t.Fatal("Get() error = nil, want error")
 		}