Reconcile Karte persistence on Cloudflare D1

[sarthakagrawal927]

What changed

• replaced the two remaining Turso-backed operator scripts with a shared, local-by-default Wrangler D1 boundary
• made production D1 access explicit through --remote and kept isolated local state available through --persist-to
• removed the now-unused @libsql/client production dependency and OpenNext externals
• corrected current documentation and public stack descriptions that still described Turso as authoritative
• added focused SQL binding, target-selection, and aggregate-rebuild tests

Why

Karte's production runtime and Better Auth data already use the linkchat-auth D1 binding, but two documented scripts, one dependency, and several current descriptions still assumed Turso. This reconciles the maintained repository with the live D1 architecture without changing production resources or data.

Validation

• isolated local D1: all 11 migrations plus four demo profiles
• local aggregate rebuild and profile-enrichment write
• PRAGMA foreign_key_check: no violations
• pnpm check
• pnpm typecheck
• pnpm test — 88 passing
• pnpm docs:check — 0 errors, 8 pre-existing archive warnings
• pnpm build
• git diff --check

No remote D1 query/write, schema change, resource creation, binding mutation, deployment, secret change, or Turso mutation was performed.

The dependency audit still reports existing advisories and strict Knip still reports the unrelated normalizePath unused export; neither was widened into this migration.

Closes #48