Pipeline Workspace.hs: worktree pool management

Create Omni/Pipeline/Workspace.hs - worktree pool management.

Depends on: Omni/Pipeline/Core.hs, Omni/Pipeline/Git.hs

Manages per-task dev worktrees and the persistent integration worktree.

Types:

• WorkspacePool: TVar (Map Text FilePath) for active workspaces, max concurrency, root path

Functions:

• newPool :: PipelineConfig -> IO WorkspacePool
• acquireWorkspace :: WorkspacePool -> Text -> Text -> IO (Either Text FilePath)

-- (pool, taskId, baseBranch) -> creates worktree, returns path

• releaseWorkspace :: WorkspacePool -> Text -> IO ()

-- removes worktree and deletes task branch

• resetWorkspace :: WorkspacePool -> Text -> Text -> IO (Either Text FilePath)

-- deletes branch, recreates from baseBranch (for retry)

• slotsAvailable :: WorkspacePool -> IO Int
• ensureIntegrationWorktree :: WorkspacePool -> Text -> IO (Either Text FilePath)
• recoverStaleWorkspaces :: WorkspacePool -> IO ()

-- startup: scan root dir, clean up orphaned worktrees

Verify: typecheck.sh Omni/Pipeline/Workspace.hs