fix(desktop): remove accidental project tabs rollout

[SivanCola]

Summary

• remove the desktop project tab rollout from feat(desktop): update Skill page and CLI /skills picker #2928, including tab persistence, project tree, and context panel surfaces
• keep the Skill page source management UI and the CLI /skills picker intact
• preserve unrelated main-v2 desktop behavior such as MCP auth diagnosis/clearing, codegraph config status, file-ref search, persistent approvals, and macOS chrome handling

Validation

• npm run typecheck in desktop/frontend
• npm run build in desktop/frontend
• go test ./... in desktop
• env HOME=/tmp/reasonix-codex-test-home-revert-2928 REASONIX_LANG=en go test ./internal/cli ./internal/config ./internal/control
• rg -n "WorkspaceTab|ListTabs|OpenProjectTab|OpenGlobalTab|SetActiveTab|CloseTab|ContextPanel|TabBar|ProjectTree|ProjectNode|TopicMeta|CreateTopic|tabId|context inspector|project tab" desktop internal -g '*.go' -g '*.ts' -g '*.tsx' returned no matches

[chatgpt-codex-connector]

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[esengine]

Agreed on dropping the unfinished tabs before release — thanks @SivanCola. Carried this forward in #3011, rebased onto current main-v2, but the raw revert re-undid two fixes that landed on top of #2928: it reverted #3003's model-switch hardening (SetModel back to close-before-build → dead controller on a failed switch) and stripped #2997's macOS window chrome from the frontend. #3011 keeps your tab removal and restores both (plus preserves #3009). Closing in favor of it.