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

[HandSonic]

Related issue

Closes #1914

Summary

Completes the Snowflake database-plugin portion of the identifier and literal escaping work.

• Adds a Snowflake identifier processor with conditional SPI quoting, unconditional DDL quoting, case folding, reserved-word handling, embedded-quote escaping, and exact quote/remove round trips.
• Routes metadata, manager, builder, column-type, and index-type SQL generation through the processor.
• Adds closed guards for default expressions, column types, index definitions, clustering clauses, sort orders, and other non-escapable SQL fragments.
• Preserves inherited DML behavior while covering Snowflake-specific metadata and DDL paths.
• Expands regression coverage for case folding, reserved words, boundary quotes, unknown types, defaults, indexes, clustering clauses, and adversarial metadata names.

Affected surfaces

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

Verification

• Commands and results:
  • mvn -pl chat2db-community-plugins/chat2db-community-snowflake -am clean test -Dmaven.test.skip=false -DskipTests=false
  • Result: BUILD SUCCESS across 9 reactor modules; 797 tests passed in tested modules, including Snowflake 28/28, MySQL 653/653, SPI 90/90, and tools 26/26.
  • git diff --check origin/main...HEAD: passed.
• Manual verification: Source-level generated-SQL review completed. No live Snowflake instance was used.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: No public API or stored-data schema change. Implements the existing shared ISQLIdentifierProcessor contract.
• Database or driver compatibility: Snowflake case folding and reserved words now determine conditional quoting; metadata and DDL paths retain exact names through unconditional quoting.
• Network, privacy, or security: No network or privacy change. Reduces malformed SQL and identifier/literal injection risk in generated Snowflake SQL.
• Community / Local / Pro boundary: Community Snowflake plugin only; Local and Pro consume the Community plugin behavior without product-specific code changes.
• Backward compatibility: Existing valid unquoted identifiers and supported SQL expressions remain accepted; malformed or ambiguous raw fragments now fail closed.

Reviewer map

• Start here: SnowflakeIdentifierProcessor, SnowflakeSqlGuards, and SnowflakeIdentifierProcessorTest, then review metadata and builder call sites.
• Failure condition: quote/remove loses raw identifier text, case folding changes identity, generated SQL exposes metadata outside identifier or literal boundaries, or legal Snowflake defaults/types/cluster clauses stop rendering.
• Rollback or disable path: Revert this PR; no migration or persisted-data rollback is required.

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: Substantial AI-assisted maintainer revision and test expansion; all final changes were source-reviewed and verified with the commands above.

[openai0229]

Rebased on the latest main and verified the complete Snowflake identifier/literal handling path. The clean 9-module reactor passes, including Snowflake 28/28, MySQL 653/653, SPI 90/90, and tools 26/26.