Related issue

Closes #1914

Summary

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

• Adds SQLite reserved-word handling and preserves the shared always-quote/remove round-trip contract for plain, quoted, embedded-delimiter, blank, and qualified-name inputs.
• Uses unconditional identifier quoting across metadata, export, create/alter/index, inherited select/count/insert/update/drop, and DML template paths.
• Replaces permissive type/default regular expressions with quote-aware balanced scanning that preserves legal nested SQLite expressions while rejecting comments, statement boundaries, top-level commas, unbalanced input, and appended column constraints.
• Makes SQLite default-value support reachable for built-in affinity types and preserves legal functions such as strftime(...) and json_extract(...).
• Escapes metadata lookup literals, flattens all supported line terminators in generated -- comments, and keeps null database qualifiers out of generated SQL.
• Corrects SQLite SELECT template generation so it emits FROM rather than the malformed shared FROM where constant.

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-sqlite -am clean test -DskipTests=false -Dmaven.test.skip=false -Dsurefire.failIfNoSpecifiedTests=false
  • Result: BUILD SUCCESS across 9 reactor modules; 791 tests passed in tested modules, including SQLite 22/22, MySQL 653/653, SPI 90/90, and tools 26/26.
  • git diff --check origin/main...HEAD: passed.
• Manual verification: Executed representative quoted CREATE TABLE, INSERT, UPDATE, CREATE INDEX, and SELECT statements with /usr/bin/sqlite3 :memory:; the final query returned updated.
• UI evidence: N/A

Risk and compatibility

• Public API or stored data: No public API or stored-data schema change. Uses the existing shared ISQLIdentifierProcessor contract.
• Database or driver compatibility: Conditional SPI quoting remains available for completion/matching; metadata-driven generated SQL always quotes raw identifiers. Legal SQLite affinity types, collations, literals, and nested default expressions are covered by regression tests and CLI execution.
• Network, privacy, or security: No network or privacy change. Reduces malformed SQL and identifier/literal injection risk in generated metadata, DDL, export, and DML paths.
• Community / Local / Pro boundary: Community SQLite plugin only; Local and Pro consume the Community plugin behavior without product-specific code changes.
• Backward compatibility: Ordinary identifiers and values retain their meaning; reserved words, embedded quotes, custom type expressions, defaults, and unusual metadata names are now encoded or validated consistently.

Reviewer map

• Start here: SqliteIdentifierProcessor, SqliteSqlGuards, then SqliteBuilder, SqliteMetaData, SqliteDBManager, and the type/index enums.
• Failure condition: Quote/remove loses raw text, legal defaults/types are rewritten, generated SQL contains raw metadata identifiers/literals, null qualifiers are rendered, or DML templates are syntactically malformed.
• 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, multi-agent review, and test expansion; all final changes were source-reviewed and verified with the commands above.