fix: stabilize Windows zellij spawns

[Vaibhaav-Tiwari]

Summary

• start Windows zellij session creation without the PowerShell Start-Process wrapper and clean up failed create attempts
• delete pre-runtime seed rows on spawn failures so the reaper does not repeatedly warn about missing runtime handles
• show daemon error-envelope messages when Electron orchestrator spawn fails
• update docs to reflect that the Go rewrite currently requires zellij 0.44.3+ and does not wire runtime process yet

Fixes #327

Tests

• go test ./internal/adapters/runtime/zellij -run TestCreate
• go test ./internal/session_manager -run TestSpawn

Notes

• Focused backend tests passed locally. Full zellij Windows integration no longer hangs in create, but still fails locally with pane exited before ready; left as a remaining integration/environment check rather than blocking this focused first-run race cleanup.
• Frontend vitest could not run in this worktree because frontend/node_modules is missing config dependencies such as vitest/config and @vitejs/plugin-react.

[Vaibhaav-Tiwari]

Review verdict: APPROVE (posted as a comment because GitHub does not allow approving your own PR).

Focused, correct, and well-tested Windows zellij spawn fix. The failed-spawn rollback refactor (rollbackSpawnSeedRow) is sound: it deletes only seed-state rows and falls back to parking terminated when the row has progressed or the delete fails, and the post-MarkSpawned path correctly keeps markSpawnFailedTerminated. The added Destroy on the createSession failure path is idempotent and uses context.Background(), matching the sibling paths. Frontend apiErrorMessage refactor and tests look good; docs are updated comprehensively.

One non-blocking cleanup note inline (dead helper functions). Full review in review.md.

[Vaibhaav-Tiwari]

Now that the PowerShell Start-Process wrapper is gone, windowsCommandLine (line 27) and windowsQuoteArg (line 35) are no longer referenced by anything except each other — they're dead code. psQuote/powerShellEncodedCommand are still used by commands.go, but these two should be removed. The unused linter is enabled in .golangci.yml; it won't fire on Linux CI because of the //go:build windows tag, but it would fail a GOOS=windows lint. Non-blocking, but worth deleting in this PR.