refactor: created TSConfig hierarchy

[colecrouter]

What changed:

• Centralized common TypeScript settings in tsconfig.base.json and removed redundant fields from child configs.
• Standardized a single cross-workspace UI alias in base: "#/" → "packages/ui/src/".
• Configured SvelteKit apps to use the same alias via kit.alias:
  • apps/whispering/svelte.config.js
  • apps/sh/svelte.config.js
  • apps/epicenter/svelte.config.js
• Preserved $lib by not defining tsconfig "paths" in SvelteKit projects; SvelteKit’s generator remains the source of truth.
• For NodeNext libraries, set "moduleResolution": "NodeNext" to avoid TS5095 when inheriting bundler settings.

Intended usage

• Non‑SvelteKit workspaces import UI internals with "#/…".
• SvelteKit apps also import with "#/…"; alias is provided by kit.alias (see links above).
• Keep using $lib inside SvelteKit for app-local imports.

Rationale

• Consistency - no surprises
• Extensibility - future shared changes
• Reliability - svelte-check aligns with IDE, $lib remains intact
• Clarity - child tsconfigs only declare environment/build specifics
• Minimality: smallest config surface

Scope

• Config-only changes.
• mcp-adapters excluded per request.
• Pinned TypeScript 5.8.3 for checks.