feat: Add Iceberg REST Catalog server and admin UI (#8175)

* feat: Add Iceberg REST Catalog server

Implement Iceberg REST Catalog API on a separate port (default 8181)
that exposes S3 Tables metadata through the Apache Iceberg REST protocol.

- Add new weed/s3api/iceberg package with REST handlers
- Implement /v1/config endpoint returning catalog configuration
- Implement namespace endpoints (list/create/get/head/delete)
- Implement table endpoints (list/create/load/head/delete/update)
- Add -port.iceberg flag to S3 standalone server (s3.go)
- Add -s3.port.iceberg flag to combined server mode (server.go)
- Add -s3.port.iceberg flag to mini cluster mode (mini.go)
- Support prefix-based routing for multiple catalogs

The Iceberg REST server reuses S3 Tables metadata storage under
/table-buckets and enables DuckDB, Spark, and other Iceberg clients
to connect to SeaweedFS as a catalog.

* feat: Add Iceberg Catalog pages to admin UI

Add admin UI pages to browse Iceberg catalogs, namespaces, and tables.

- Add Iceberg Catalog menu item under Object Store navigation
- Create iceberg_catalog.templ showing catalog overview with REST info
- Create iceberg_namespaces.templ listing namespaces in a catalog
- Create iceberg_tables.templ listing tables in a namespace
- Add handlers and routes in admin_handlers.go
- Add Iceberg data provider methods in s3tables_management.go
- Add Iceberg data types in types.go

The Iceberg Catalog pages provide visibility into the same S3 Tables
data through an Iceberg-centric lens, including REST endpoint examples
for DuckDB and PyIceberg.

* test: Add Iceberg catalog integration tests and reorg s3tables tests

- Reorganize existing s3tables tests to test/s3tables/table-buckets/
- Add new test/s3tables/catalog/ for Iceberg REST catalog tests
- Add TestIcebergConfig to verify /v1/config endpoint
- Add TestIcebergNamespaces to verify namespace listing
- Add TestDuckDBIntegration for DuckDB connectivity (requires Docker)
- Update CI workflow to use new test paths

* fix: Generate proper random UUIDs for Iceberg tables

Address code review feedback:
- Replace placeholder UUID with crypto/rand-based UUID v4 generation
- Add detailed TODO comments for handleUpdateTable stub explaining
  the required atomic metadata swap implementation

* fix: Serve Iceberg on localhost listener when binding to different interface

Address code review feedback: properly serve the localhost listener
when the Iceberg server is bound to a non-localhost interface.

* ci: Add Iceberg catalog integration tests to CI

Add new job to run Iceberg catalog tests in CI, along with:
- Iceberg package build verification
- Iceberg unit tests
- Iceberg go vet checks
- Iceberg format checks

* fix: Address code review feedback for Iceberg implementation

- fix: Replace hardcoded account ID with s3_constants.AccountAdminId in buildTableBucketARN()
- fix: Improve UUID generation error handling with deterministic fallback (timestamp + PID + counter)
- fix: Update handleUpdateTable to return HTTP 501 Not Implemented instead of fake success
- fix: Better error handling in handleNamespaceExists to distinguish 404 from 500 errors
- fix: Use relative URL in template instead of hardcoded localhost:8181
- fix: Add HTTP timeout to test's waitForService function to avoid hangs
- fix: Use dynamic ephemeral ports in integration tests to avoid flaky parallel failures
- fix: Add Iceberg port to final port configuration logging in mini.go

* fix: Address critical issues in Iceberg implementation

- fix: Cache table UUIDs to ensure persistence across LoadTable calls
  The UUID now remains stable for the lifetime of the server session.
  TODO: For production, UUIDs should be persisted in S3 Tables metadata.

- fix: Remove redundant URL-encoded namespace parsing
  mux router already decodes %1F to \x1F before passing to handlers.
  Redundant ReplaceAll call could cause bugs with literal %1F in namespace.

* fix: Improve test robustness and reduce code duplication

- fix: Make DuckDB test more robust by failing on unexpected errors
  Instead of silently logging errors, now explicitly check for expected
  conditions (extension not available) and skip the test appropriately.

- fix: Extract username helper method to reduce duplication
  Created getUsername() helper in AdminHandlers to avoid duplicating
  the username retrieval logic across Iceberg page handlers.

* fix: Add mutex protection to table UUID cache

Protects concurrent access to the tableUUIDs map with sync.RWMutex.
Uses read-lock for fast path when UUID already cached, and write-lock
for generating new UUIDs. Includes double-check pattern to handle race
condition between read-unlock and write-lock.

* style: fix go fmt errors

* feat(iceberg): persist table UUID in S3 Tables metadata

* feat(admin): configure Iceberg port in Admin UI and commands

* refactor: address review comments (flags, tests, handlers)

- command/mini: fix tracking of explicit s3.port.iceberg flag
- command/admin: add explicit -iceberg.port flag
- admin/handlers: reuse getUsername helper
- tests: use 127.0.0.1 for ephemeral ports and os.Stat for file size check

* test: check error from FileStat in verify_gc_empty_test

weed/command/admin.go

@@ -42,6 +42,7 @@ type AdminOptions struct {
 	readOnlyUser     *string
 	readOnlyPassword *string
 	dataDir          *string
+	icebergPort      *int
 }
 
 func init() {
@@ -56,6 +57,7 @@ func init() {
 	a.adminPassword = cmdAdmin.Flag.String("adminPassword", "", "admin interface password (if empty, auth is disabled)")
 	a.readOnlyUser = cmdAdmin.Flag.String("readOnlyUser", "", "read-only user username (optional, for view-only access)")
 	a.readOnlyPassword = cmdAdmin.Flag.String("readOnlyPassword", "", "read-only user password (optional, for view-only access; requires adminPassword to be set)")
+	a.icebergPort = cmdAdmin.Flag.Int("iceberg.port", 8181, "Iceberg REST Catalog port (0 to hide in UI)")
 }
 
 var cmdAdmin = &Command{
@@ -211,7 +213,7 @@ func runAdmin(cmd *Command, args []string) bool {
 	}()
 
 	// Start the admin server with all masters (UI enabled by default)
-	err := startAdminServer(ctx, a, true)
+	err := startAdminServer(ctx, a, true, *a.icebergPort)
 	if err != nil {
 		fmt.Printf("Admin server error: %v\n", err)
 		return false
@@ -222,7 +224,7 @@ func runAdmin(cmd *Command, args []string) bool {
 }
 
 // startAdminServer starts the actual admin server
-func startAdminServer(ctx context.Context, options AdminOptions, enableUI bool) error {
+func startAdminServer(ctx context.Context, options AdminOptions, enableUI bool, icebergPort int) error {
 	// Set Gin mode
 	gin.SetMode(gin.ReleaseMode)
 
@@ -281,7 +283,7 @@ func startAdminServer(ctx context.Context, options AdminOptions, enableUI bool)
 	}
 
 	// Create admin server
-	adminServer := dash.NewAdminServer(*options.master, nil, dataDir)
+	adminServer := dash.NewAdminServer(*options.master, nil, dataDir, icebergPort)
 
 	// Show discovered filers
 	filers := adminServer.GetAllFilers()