refactor(core): add context to git interfaces and remove type assertions

[indaco]

Description

• Add context.Context as the first parameter to all GitTagOperations and GitCommitOperations in core/interfaces.go
• Update all implementations in tagmanager/git.go to use exec.CommandContext for cancellable subprocess execution
• Promote IsEnabled(), IsAutoCreateEnabled(), GetConfig(), CommitChanges() onto plugin interfaces (TagManager, VersionValidator, ReleaseGate)
• Eliminate all type assertions in commands/bump/helpers.go and commands/depsync/sync.go
• Update all mocks (core/mocks.go, tagmanager mock files) to match new signatures

Related Issue

Notes for Reviewers