迁移到 SQLite 事实源并加入原生备份

[ApeCodeLab]

Summary

• Treat SQLite as FinSight's authoritative local store during normal use.
• Add finsight backup create and finsight backup verify for native SQLite recovery copies.
• Make doctor read-only for SQLite health checks.
• Prevent init --demo from replacing an already populated portfolio database.
• Keep the plain-text ledger only as explicit, lossy legacy interoperability.
• Update public English/Chinese docs, CLI docs, examples, and Agent skill to match.

Privacy boundary

• No personal account data, real holdings, 九坤 material, internal endpoints, or private OCR scripts are included.
• The existing public ApeCode/BytePass history is intentionally unchanged.

MVP boundary

This PR is for a single-user, local-only, Agent-first MVP. It does not add multi-user auth, distributed transactions, hostile-process hardening, or ABA/TOCTOU defenses.

Verification

• pnpm -r test
• pnpm typecheck
• pnpm -r build
• CI skill-drift check
• git diff --check
• Isolated temporary-DB smoke test: init → doctor → backup create → backup verify

Review boundary

Please review this as one migration slice. Do not merge unrelated FX, screenshot/OCR, personal-data, package-release, or security-hardening work into this PR.