Unify the release artifacts.

[Gujiawei-Edinburgh]

This change unifies release artifacts by packaging both .sh and .bat scripts into the single .tar.gz output and dropping the separate Windows ZIP build. The Maven assembly
configuration now includes both script types in the bin directory for the standalone artifact, and the Windows-specific assembly descriptor and execution are removed. This
keeps one release format while still supporting both OS-specific launch scripts.

Final bin/ layout:
bin
├── bifromq-start.bat
├── bifromq-start.sh
├── bifromq-stop.bat
├── bifromq-stop.sh
├── pid.bat
├── standalone.bat
└── standalone.sh

[coveralls]

Pull Request Test Coverage Report for Build 21463864592

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 34 unchanged lines in 9 files lost coverage.
• Overall coverage increased (+0.05%) to 65.232%

---

Files with Coverage Reduction	New Missed Lines	%
org/apache/bifromq/basecluster/memberlist/HostMemberList.java	1	93.43%
org/apache/bifromq/basecluster/transport/TCPTransport.java	1	87.06%
org/apache/bifromq/basekv/raft/RaftNodeStateLeader.java	2	86.43%
org/apache/bifromq/dist/trie/TopicFilterIterator.java	2	75.46%
org/apache/bifromq/basekv/raft/exception/LeaderTransferException.java	3	81.25%
org/apache/bifromq/dist/trie/NTopicFilterTrieNode.java	3	88.24%
org/apache/bifromq/basekv/store/range/KVRangeFSM.java	6	82.38%
org/apache/bifromq/basekv/raft/RaftNodeStateFollower.java	8	83.19%
org/apache/bifromq/inbox/store/InboxStoreCoProc.java	8	79.14%

Totals
Change from base Build 21463822173:	0.05%
Covered Lines:	27887
Relevant Lines:	41280

---

💛 - Coveralls

[popduke]

LGTM