perf(web): split heavy UI and guarded Tauri modules

[Tutitoos]

Roadmap reference

Phase 8 - quality hardening and release readiness.

Objective

Reduce the initial web payload and remove Vite ineffective dynamic-import warnings while preserving authenticated web and Tauri desktop behavior.

Scope

• Lazy-load route- and interaction-specific UI such as administration, conversations, and the rich composer.
• Keep Tauri APIs outside the ordinary web startup path by using guarded dynamic imports consistently.
• Add regression coverage for lazy loading and desktop command helpers.
• Record production build chunk sizes before and after.

Tasks

• Split heavy UI modules at stable Suspense boundaries.
• Consolidate guarded Tauri invocation without static core imports.
• Verify all routes and composer/conversation interactions.
• Run the complete web, browser, and production-build validation.

Acceptance criteria

• The initial JavaScript chunk is below the current ~743 kB baseline.
• The INEFFECTIVE_DYNAMIC_IMPORT warning for @tauri-apps/api/core is gone.
• Admin, inbox, conversation, composer, authentication, and desktop tests remain green.
• No new loading-state accessibility regression is introduced.

Validation

• bun run --cwd apps/web typecheck
• bun run --cwd apps/web test
• bun run --cwd apps/web test:e2e
• bun run --cwd apps/web build
• Inspect emitted chunk sizes and warnings.

Dependencies

• Follows fix(web): complete bilingual workspace controls #190 / PR fix(web): complete bilingual workspace controls #191.

Risks

• Incorrect lazy boundaries can cause visible flashes or defer runtime errors until interaction.
• Tauri imports must remain unreachable in ordinary browser sessions.

Exclusions

• No new product features or visual redesign.
• No dependency upgrades.
• No backend protocol changes.