fix: use dialect-specific issue list LIKE escape

[zhangyangyu]

Description

Fix issue-list title_prefix SQL generation for MySQL/TiDB by using the existing dialect-specific LIKE escape clause helper instead of hard-coding the non-MySQL escape literal.

The public CI failure was in the REST aggregate issue-list filter path, where TiDB rejected a generated ESCAPE '\' clause. This updates the issue-list query builder to receive the active GORM database so it can emit the MySQL/TiDB form, and adds builder coverage for both issue and pull request title filters.

Tracking

N/A

Tests

• git diff --check
• go test ./internal/service -run 'TestBuildIssueListPageQueryUsesMySQLLikeEscapeClause|TestWikiSearchLikeEscapeClauseByDialect'
• go test ./internal/rest -run '^$'

Local note: attempted to run the TiDB-backed REST reproduction locally, but the local TiDB playground failed to start on this machine. PR CI should cover the full REST unit suite.

Risks / Reviewer Notes

Low risk. The change only alters the SQL escape clause used by title_prefix issue-list filters; non-MySQL dialects keep the existing fallback clause.

SSOT Drift Prevention Checklist

• Checked that this PR does not violate boundaries in docs/architecture.md or docs/module-contracts.md
• If this PR changes package structure or dependencies, updated the relevant SSOT doc
• If this PR changes test conventions or coverage expectations, updated docs/test-strategy.md
• If this PR changes CI, smoke, regression, or workflow expectations, updated docs/ci.md