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/server.go

@@ -158,6 +158,7 @@ func init() {
 	s3Options.port = cmdServer.Flag.Int("s3.port", 8333, "s3 server http listen port")
 	s3Options.portHttps = cmdServer.Flag.Int("s3.port.https", 0, "s3 server https listen port")
 	s3Options.portGrpc = cmdServer.Flag.Int("s3.port.grpc", 0, "s3 server grpc listen port")
+	s3Options.portIceberg = cmdServer.Flag.Int("s3.port.iceberg", 8181, "Iceberg REST Catalog server listen port (0 to disable)")
 	s3Options.domainName = cmdServer.Flag.String("s3.domainName", "", "suffix of the host name in comma separated list, {bucket}.{domainName}")
 	s3Options.allowedOrigins = cmdServer.Flag.String("s3.allowedOrigins", "*", "comma separated list of allowed origins")
 	s3Options.tlsPrivateKey = cmdServer.Flag.String("s3.key.file", "", "path to the TLS private key file")