fix(translate): repair dialect detection — UPSERT routing, whitespace, MySQL quoting, dead code
CRITICAL BUG-1: UPSERT routing generated invalid ON CONFLICT for MySQL,
MSSQL, Snowflake, Oracle, DuckDB. Now uses explicit UPSERT_SUPPORTED_DIALECTS
({'postgresql', 'redshift'}) — unknown dialects get plain INSERT.
BUG-2: _extract_dialect did not strip whitespace, inconsistent with
get_dialect_from_database. Fixed guard + normalized value.
BUG-3: Whitespace-only input (' ', '\n') returned itself instead of 'unknown'.
BUG-4: Dead code — removed 'greenplum' from POSTGRESQL_DIALECTS
(always normalized to 'postgresql').
BUG-5: MySQL identifier quoting used double quotes instead of native backticks.
Added BACKTICK_DIALECTS set.
MOCK-FIX: test_at_least_one_row_per_batch patched wrong path
(executor.estimate_token_budget -> _batch_sizer.estimate_token_budget).
Adds 131 orthogonal tests covering all 4 dialect detection code paths
across input formats, normalization, routing, quoting, encoding,
schema validation, and cross-component consistency.
busya
18f88a6928