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/storage/verify_gc_empty_test.go

@@ -0,0 +1,74 @@
+package storage
+
+import (
+	"os"
+	"testing"
+
+	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
+	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
+)
+
+func TestCompactionToEmpty(t *testing.T) {
+	dir := t.TempDir()
+
+	// 1. Create a new volume
+	v, err := NewVolume(dir, dir, "", 678, NeedleMapInMemory, &super_block.ReplicaPlacement{}, &needle.TTL{}, 0, needle.GetCurrentVersion(), 0, 0)
+	if err != nil {
+		t.Fatalf("volume creation: %v", err)
+	}
+	defer v.Close()
+
+	// 2. Write a few needles
+	numNeedles := 5
+	for i := 1; i <= numNeedles; i++ {
+		n := newRandomNeedle(uint64(i))
+		_, _, _, err := v.writeNeedle2(n, true, false)
+		if err != nil {
+			t.Fatalf("write needle %d: %v", i, err)
+		}
+	}
+
+	// 3. Delete all of them
+	for i := 1; i <= numNeedles; i++ {
+		n := newEmptyNeedle(uint64(i))
+		_, err := v.deleteNeedle2(n)
+		if err != nil {
+			t.Fatalf("delete needle %d: %v", i, err)
+		}
+	}
+
+	// 4. Run compaction
+	err = v.Compact2(0, 0, nil)
+	if err != nil {
+		t.Fatalf("compaction: %v", err)
+	}
+
+	// 5. Commit compaction
+	err = v.CommitCompact()
+	if err != nil {
+		t.Fatalf("commit compaction: %v", err)
+	}
+
+	// 6. Verify the resulting .dat file size
+	datSize, _, err := v.FileStat()
+	if err != nil {
+		t.Fatalf("file stat: %v", err)
+	}
+	if datSize != super_block.SuperBlockSize {
+		t.Errorf("expected dat file size %d, got %d", super_block.SuperBlockSize, datSize)
+	}
+
+	// 7. Verify index file size (should be 0 or at least no entries)
+	if v.nm.FileCount() != 0 {
+		t.Errorf("expected 0 files in needle map, got %d", v.nm.FileCount())
+	}
+
+	// Check if the file itself exists and is empty (except for superblock)
+	info, err := os.Stat(v.FileName(".dat"))
+	if err != nil {
+		t.Fatalf("stat dat file: %v", err)
+	}
+	if info.Size() != int64(super_block.SuperBlockSize) {
+		t.Fatalf("dat file physical size mismatch: expected %d, got %d", super_block.SuperBlockSize, info.Size())
+	}
+}