test: Tag 16 slow integration tests with build tags

Identified and tagged obviously-slow integration tests with
`//go:build integration` to exclude them from default test runs.

This is step 1 of fixing test performance. The real fix is in
bd-1rh: refactoring tests to use shared DB setup instead of
creating 279 separate databases.

Tagged files:
- cmd/bd: 8 files (CLI tests, git ops, performance benchmarks)
- internal: 8 files (integration tests, E2E tests)

Issues:
- bd-1rh: Main issue tracking test performance
- bd-c49: Audit all tests and create grouping plan (next step)
- bd-y6d: POC refactor of create_test.go

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

internal/beads/routing_integration_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package beads_test
 
 import (

internal/compact/compactor_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package compact
 
 import (

internal/daemon/discovery_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package daemon
 
 import (

internal/importer/external_ref_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package importer
 
 import (

internal/rpc/comments_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package rpc
 
 import (

internal/rpc/version_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package rpc
 
 import (

internal/storage/sqlite/adaptive_e2e_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package sqlite
 
 import (

internal/testutil/fixtures/fixtures_test.go

@@ -1,3 +1,6 @@
+//go:build integration
+// +build integration
+
 package fixtures
 
 import (