Add T006 select-into-without-typed-fields (T-SQL runtime schema inference)

[Pawansingh3889]

Closes #43.

T-SQL accepts SELECT * INTO new_table FROM source and derives the destination schema from whatever the source produces at execution time. If the source columns change shape (a column added, a type widened, an index swapped) the destination silently adopts those changes, and any code reading from new_table finds the schema has shifted underneath it. Delayed, hard-to-trace data-integrity bugs.

Recommended pattern is the explicit form: CREATE TABLE new_table (col1 TYPE, ...) then INSERT INTO new_table (col1, ...) SELECT col1, ... FROM source. The destination schema lives in source control and a contract breakage shows up as a compile error rather than silently propagated wrong types.

Severity is warning, modelled on T001 / T005. The rule fires only on the wildcard form. The explicit-column variant SELECT col1, col2 INTO target FROM source still derives types from source columns but at least names what is being copied; it stays a green path here and is covered by the contracts pack at C001 / C003 if a column type drifts.

Implementation is a one-pattern regex \bSELECT\s+\*\s+INTO\s+\S+, modelled on the shape of T001 and T005.

Samples:

-- Flagged
SELECT * INTO staging_orders FROM orders;
SELECT * INTO archive_2024 FROM orders WHERE year = 2024;
SELECT *
INTO staging_orders
FROM orders;

-- Not flagged
SELECT order_id, customer_id INTO staging_orders FROM orders;  -- recommended pass form from #43
SELECT id INTO ids FROM orders;
SELECT * FROM orders WHERE id = 1;                              -- no INTO
SELECT @x = COUNT(*) FROM orders;                                -- T-SQL local-variable assignment
WITH s AS (SELECT * FROM orders) SELECT id FROM s;               -- CTE without INTO

Tests: 10 new methods on test_tsql.py covering the issue example, multi-line layout, lowercase, the recommended pass form, single-column INTO, SELECT * without INTO, T-SQL variable assignment, CTE without INTO, and a message-content assertion. test_tsql.py 28 pass (was 18). Full suite: 233 pass, 1 skipped, no regressions.

Four commits on this branch. The first adds the rule in tsql.py and registers it in __init__.py; registry counts move to 41 total and 30 warnings. The second adds the tests. The third documents the rule in CHANGELOG under [Unreleased] Added. The fourth adds the T006 row to the README rule table.

Commits signed (ED25519).