arch: restructure monorepo into domain-driven packages

[kayodebristol]

Summary

Restructure the repository from the current flat package layout into a domain-driven architecture with clear ownership boundaries.

Target Package Structure

packages/
  domain/          — Pure types, invariants, value objects
  ledger/          — Accounts, balances, postings, transfers, snapshots, reconciliation
  ingestion/       — CSV/OFX/QFX adapters, file templates, row parsing, provenance
  resolution/      — Merchant resolution, alias graph, duplicate clustering, transfer detection
  analytics/       — Trend analysis, debt scenarios, budget vs actual, burn rate
  advice/          — Plan generation, recommendation ranking, scenario comparisons
  ai-providers/    — LLM provider abstraction (demoted from center stage)
  mcp-server/      — MCP tools exposing stable domain/analytics operations

Current State

• packages/shared → becomes packages/domain
• packages/financial-tools → split into ledger, ingestion, resolution, analytics
• packages/ai-integration → becomes packages/ai-providers (utility, not core)
• packages/mcp-server → stays, but depends on real domain operations
• packages/vscode-extension → keep as-is for now

Principles

• Each package has a single clear owner domain
• No cross-package circular dependencies
• AI is a supporting capability, not the architecture
• Domain types are strict — no "optional everything" models

Acceptance

• All 8 packages created with clear boundaries
• Existing code migrated to correct packages
• Package dependency graph is acyclic
• Each package has its own tsconfig, tests, exports