perf(components): lazy-load settings tab bodies off the shell

[slashdevcorpse]

Related issue

Closes #493

Problem / pressure

Electron does not enable TanStack auto code-splitting. routeTree.gen.ts statically imports every settings route, and those files plus DesktopSettingsModal statically import tab bodies (MCP, billing, stats, agent config). Authenticated-shell cold start parses that graph before Settings opens.

Summary

Settings tab bodies load through lazy() from each route file, matching archive.tsx, and from SettingsTabContent in the desktop modal. Navigate-only legacy routes (general, stats, devices, my-machines, agent-config) are unchanged. Whole-app autoCodeSplitting is not enabled.

Before / after

Before	After
MCP/billing/stats/agent-config modules parse with the shell.	Those modules load when the tab or modal tab mounts.
Closed desktop settings dialog still imported every tab.	Dialog chrome stays; tab bodies lazy() behind Suspense.

Test plan

• pnpm exec prettier --write on the changed settings routes and desktop-settings-modal.tsx.
• No Electron bundle comparison in this PR. No live first-open timing.

Context handoff

Instructions for reviewing agents

• Review focus: lazy() wrappers in settings/*.tsx (except Navigate-only legacy routes) and desktop-settings-modal.tsx SettingsTabContent.
• Decisions to challenge: Per-tab lazy() instead of enabling autoCodeSplitting in electron.vite.config.ts. Suspense fallback={null} while a tab chunk loads.
• Plausible failures / evidence gaps: First Settings open still pays for the default account tab. No before/after chunk list from an Electron renderer build.

Authoring context

• User goal / directives: Code-split settings tab modules off the authenticated desktop shell without duplicating perf(components): stage mobile background sync so the app stays usable #317.
• Constraints / non-goals: Do not enable whole-app router auto-splitting. Do not change settings behavior or MCP catalog reads on chat landing.
• Risk-bearing decisions: A brief empty panel while a tab chunk loads (fallback={null}).
• Destructive or irreversible behavior: None.
• Deliberately not done or tested: Electron production bundle sizes. Mobile settings layout chrome. Command palette split.
• Unknowns / confidence: High that static imports of tab bodies are gone from these files. Medium on measured cold-start delta without a bundle dump.

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[github-actions]

@slashdevcorpse, this pull request was closed because it did not meet Lody's contribution requirements for 7 days.

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