Feat v0.7.6 code hygiene + test coverage

Clean up channels-era dead code, align migrations, add 92 tests,
and fix backup download + admin storage tab bugs before v0.8.x
kernel expansion.

Critical fixes:
- Remove `channels` from allowedViews in db_module.go
- Fix 5 dead API routes in workflow.html → public workflow API
- Fix RenderWorkflow handler to use route param as entry token

Dead code removal:
- Delete SeedTestChannel(), RunContext.ChannelID, webhook.ChannelID
- Fix stale comments in storage.go, prometheus.go, workflow_module.go

Migration hygiene:
- Add SQLite placeholder 013_cluster_registry.sql, renumber to 014
- Compat rename in migrate.go for existing SQLite databases
- Document missing migration 008 in both 009 files

Test coverage:
- 82 workflow routing tests (all operators, branch rules, stage resolution)
- 10 middleware tests (permissions, admin, rate limiter)

Bug fixes:
- Remove dead Admin Storage tab from System category
- Fix backup download: sw.auth.token() → sw.auth._getToken()

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/database/migrate.go

@@ -74,6 +74,12 @@ func Migrate() error {
 		}
 	}
 
+	// v0.7.6: SQLite 013_test_runner_type.sql was renumbered to 014 to
+	// align with PG migration numbering. Mark as applied if the old name exists.
+	if !IsPostgres() {
+		DB.Exec("UPDATE schema_migrations SET version = '014_test_runner_type.sql' WHERE version = '013_test_runner_type.sql'")
+	}
+
 	// Apply pending migrations.
 	applied := 0
 	for _, file := range files {