feat: add etcd v3 database plugin (#343)

* feat: add etcd v3 database plugin with prefix-tree key browsing

Add a new etcd driver plugin using the v3 HTTP/JSON gateway (no C bridge).
Supports prefix-tree sidebar navigation, etcdctl-compatible editor syntax,
lease management, bounded watch, mTLS, auth/RBAC, and cluster info.

Also fixes QueryTab.buildBaseTableQuery to use plugin's buildBrowseQuery
when available, so NoSQL plugins get table-specific initial queries
instead of hardcoded SCAN commands.

* fix: address PR review for etcd plugin (critical + major issues)

* fix: unify sidebar and data grid save pipelines for all database drivers

* fix: prepend browse prefix to etcd insert keys

* fix: etcd plugin audit fixes, missing features, and comprehensive tests

* fix: use force cast for SecIdentity CoreFoundation type (always succeeds)

* fix: address second round of PR review feedback

* build: extract etcd plugin from app bundle for registry distribution

* fix: address third round of PR review feedback

Author: datlechin

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- etcd v3 plugin with prefix-tree key browsing, etcdctl syntax editor, lease management, watch, mTLS, auth, and cluster info
 - Save Changes button in toolbar for committing pending data edits
 - Confirmation dialog before deleting a connection
 - Confirmation dialog before sort, pagination, filter, or search discards unsaved edits