feat: materialize workspace project sessions

[neversettle17-101]

Summary

• add an optional workspace-project adapter contract for root-plus-child repo worktree materialization
• create workspace project sessions as one root worktree plus one child worktree per registered workspace repo, all on the same session branch
• persist session_worktrees rows for every created repo and roll back all worktrees when spawn fails after materialization

Scope

This is the first backend slice for #2222. It does not yet implement multi-repo kill/restore/save lifecycle, SCM/PR aggregation across child repos, or frontend/API exposure.

Tests

• cd backend && go test ./internal/session_manager ./internal/adapters/workspace/gitworktree
• cd backend && go test ./...

Closes part of #2222

[neversettle17-101]

Claiming this PR to continue the remaining backend workspace-project work from #2222. I’ll keep the next slice focused and update this branch with tests.

[neversettle17-101]

Correction to the previous comment: shell expansion stripped some backticked text while posting.

Pushed CI fixes in aad293b.

What changed:

• added the missing comments for exported workspace project port types that revive flagged
• fixed Unix process liveness so ao stop treats zombie daemon children as stopped; this resolves the native E2E TestE2E_Lifecycle timeout where the daemon had exited but the test parent had not reaped it yet
• added a processalive regression test for zombie handling

Local verification:

• cd backend && go test -tags e2e -run TestE2E_Lifecycle -v ./internal/cli
• cd backend && go test -tags e2e ./internal/cli
• cd backend && go test ./internal/processalive ./internal/session_manager ./internal/adapters/workspace/gitworktree
• npm run lint

Remaining #2222 work is still separate from this PR's current backend slice: multi-worktree teardown/restore, SCM/PR repo-aware observation and claim, root change flow, and status aggregation.