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/capture.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"strings"
 
-	"github.com/google/uuid"
 	"github.com/modelcontextprotocol/go-sdk/mcp"
 
 	"git.warky.dev/wdevs/amcs/internal/ai"
@@ -17,13 +16,13 @@ import (
 
 // EmbeddingQueuer queues a thought for background embedding generation.
 type EmbeddingQueuer interface {
-	QueueThought(ctx context.Context, id uuid.UUID, content string)
+	QueueThought(ctx context.Context, id int64, content string)
 }
 
 // MetadataQueuer queues a thought for background metadata retry. Both
 // MetadataRetryer and EnrichmentRetryer satisfy this.
 type MetadataQueuer interface {
-	QueueThought(id uuid.UUID)
+	QueueThought(id int64)
 }
 
 type CaptureTool struct {
@@ -66,7 +65,7 @@ func (t *CaptureTool) Handle(ctx context.Context, req *mcp.CallToolRequest, in C
 		Metadata: rawMetadata,
 	}
 	if project != nil {
-		thought.ProjectID = &project.ID
+		thought.ProjectID = &project.NumericID
 	}
 
 	created, err := t.store.InsertThought(ctx, thought, t.embeddings.PrimaryModel())
@@ -74,7 +73,7 @@ func (t *CaptureTool) Handle(ctx context.Context, req *mcp.CallToolRequest, in C
 		return nil, CaptureOutput{}, err
 	}
 	if project != nil {
-		_ = t.store.TouchProject(ctx, project.ID)
+		_ = t.store.TouchProject(ctx, project.NumericID)
 	}
 
 	if t.retryer != nil {