fix(generic): escape SQL identifiers and literals in metadata/DDL paths (#1914)

[HandSonic]

Related issue

Closes #1914

Summary

• Harden Generic database and table DDL template substitution against second-order SQL injection from database metadata.
• Inspect each configured SQL template before substitution: values in single-quoted placeholder positions are escaped as string-literal content, while values in bare placeholder positions must be strict identifier tokens because the Generic adapter cannot assume one dialect quote character.
• Register GenericIdentifierProcessor for SPI consumers, keeping ordinary quoteIdentifier conditional while implementing unconditional, delimiter-safe quoteIdentifierAlways with exact quote/remove round-trip behavior.
• Preserve the original database, schema, and table names for the JDBC metadata fallback; only the configured SQL-template path receives escaped template values.
• Add focused tests for DuckDB literal templates, TDengine bare-identifier templates, malicious inputs, conditional quoting, boundary delimiters, blank values, and exact round trips.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Commands and results:
  • mvn -B -f chat2db-community-server/pom.xml -pl chat2db-community-plugins/chat2db-community-generic -am clean test -Dmaven.test.skip=false -DskipTests=false -Dmaven.test.failure.ignore=false
  • Result: 13-module reactor BUILD SUCCESS; tools 26/26, SPI 90/90, MySQL 653/653, PostgreSQL 49/49, DuckDB 2/2, TDengine 1/1, Generic 15/15; zero failures, errors, or skipped tests in these modules. Elasticsearch and domain-api compiled successfully and contain no tests in this reactor.
  • git diff --check origin/main...HEAD
  • Result: passed with no whitespace errors.
• Manual verification: N/A; the affected SQL generation and identifier contracts are covered by executable unit tests, and no live Generic database is required for the template-substitution logic.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: No stored-data migration. The Generic plugin now exposes its identifier processor through the existing SPI contract; no new public endpoint is added.
• Database or driver compatibility: DuckDB single-quoted metadata lookups retain arbitrary object-name support through literal escaping. TDengine bare template positions now reject names outside [A-Za-z0-9_$]+ because Generic cannot safely infer a dialect delimiter there.
• Network, privacy, or security: Reduces second-order SQL-injection risk in Generic metadata and database-switch templates. No network or privacy behavior changes.
• Community / Local / Pro boundary: Community Generic plugin only; Local or Pro products consume the change only when built from this Community plugin.
• Backward compatibility: Normal identifiers and existing configured templates remain supported. Unsafe or dialect-ambiguous bare identifiers now fail fast instead of being interpolated into SQL.

Reviewer map

• Start here: chat2db-community-server/chat2db-community-plugins/chat2db-community-generic/src/main/java/ai/chat2db/plugin/generic/GenericSqlGuards.java, then GenericMetaData.java, GenericDBManager.java, and identifier/GenericIdentifierProcessor.java.
• Failure condition: Any configured template receives an unescaped single-quoted value, accepts an unsafe bare identifier, mutates the original JDBC fallback arguments, or violates removeIdentifierQuote(quoteIdentifierAlways(raw)).equals(raw).
• Rollback or disable path: Revert this PR. There is no feature flag or persistent-data migration.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: Maintainer used AI-assisted code review and test development; all resulting changes were source-reviewed and verified with the clean Maven reactor reported above.

[openai0229]

Maintainer review complete: Generic template values are context-aware, JDBC fallback arguments remain raw, the identifier processor satisfies the shared always-quote round-trip contract, and the 13-module clean reactor passed.