Add local TiDB smoke workflow

[okJiang]

Summary

Replaces the previous local PostgreSQL smoke lane with a TiDB-only local smoke path.

This PR now:

• removes the standalone PG workflow/lane
• adds e2e/local-tidb-smoke.sh
• adds .github/workflows/local-tidb-smoke.yml
• keeps shared API assertions in e2e/local-smoke-checks.sh

The TiDB smoke boots a local TiUP playground cluster, seeds an active tenant directly in the control-plane schema, starts mnemo-server with MNEMO_DB_BACKEND=tidb, and verifies the v1alpha2 memories API on the real TiDB backend path.

Covered flow:

• healthz and versionz
• auth failure guardrails
• create memory with direct content
• list by tag and extract the created memory ID
• keyword recall/search with confidence output
• get, update, delete, and deleted-get verification

CI

Adds .github/workflows/local-tidb-smoke.yml, triggered by PR/push changes to server, the TiDB smoke scripts, or the workflow itself, plus manual workflow_dispatch. It uploads TiDB/server/smoke logs as artifacts.

Validation

• bash -n e2e/local-smoke-checks.sh
• bash -n e2e/local-tidb-smoke.sh
• YAML parse for .github/workflows/local-tidb-smoke.yml
• Local TiUP playground + mnemo-server run: 19 / 19 passed
• GitHub Actions: Local TiDB smoke green on commit 6ffd706

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Name	Link
🔨 Latest commit	6ffd706

[okJiang]

LGTM. Clean tier 2 implementation. pgvector + direct tenant seed gives us API coverage without external dependencies. 19/19 local validation, actionlint clean, artifact upload on failure. Good follow-through on the three-tier plan.