feat(postgresql): add accurate analyzer mode for database-only analysis

[kyleconroy]

Summary

Adds an optional analyzer.accurate: true mode for PostgreSQL that bypasses the internal catalog and uses only database-backed analysis for more accurate type information.

Key Features

• Database-only type resolution: Uses PostgreSQL PREPARE statements for all column and parameter type inference
• Database-backed star expansion: Uses the expander package (from #4203) with database queries for SELECT * and RETURNING * expansion
• Schema introspection: Queries pg_catalog to build catalog structures needed for code generation (tables, columns, enums)
• No internal catalog: Skips building the internal catalog from schema files in accurate mode

Configuration

version: "2"
sql:
  - engine: postgresql
    schema: "schema.sql"
    queries: "queries/"
    database:
      uri: "postgres://localhost/mydb"  # or managed: true
    analyzer:
      accurate: true
    gen:
      go:
        package: "db"
        out: "db"

Requirements

• Accurate mode requires a database connection (database.uri or database.managed: true)
• The schema must exist in the database before running sqlc generate
• Only supported for PostgreSQL engine

Files Changed

File	Changes
internal/config/config.go	Added Accurate *bool to Analyzer struct
internal/config/v_one.json, v_two.json	Added accurate boolean to analyzer schema
internal/engine/postgresql/analyzer/analyze.go	Added IntrospectSchema(), EnsurePool(), GetColumnNames() methods
internal/compiler/engine.go	Added accurate mode detection and expander setup
internal/compiler/compile.go	Skip catalog building, introspect schema after parsing
internal/compiler/parse.go	Use expander for star expansion in accurate mode

Test plan

• [x] All existing tests pass
• [x] Code compiles without errors
• [ ] Manual testing with local PostgreSQL database

🤖 Generated with Claude Code