[luthermonson]

I found these gaps by replaying Sendy 7.1.6's includes/update.php against MySQL 8.4.11 and litewire/Turso (through ePHPm), then diffing the resulting schemas. I also replayed a sweep of the app's ~1,000 SQL statement shapes. Before this PR, the updater hit 30 failed statements on litewire. After it, the schema diff shows one difference: a unique index whose guard needs GET_LOCK, which ePHPm wires through #642.

ALTER TABLE

• Column changes go through SQLite's table rebuild. This covers MODIFY / CHANGE / ALTER [COLUMN] c {SET|DROP} {DEFAULT|NOT NULL} and ADD ... FIRST|AFTER c. ADD ... FIRST|AFTER matters because MySQL column order shows up in SHOW COLUMNS and SELECT *.
  • Translation returns a new TranslateResult::RebuildTable(ColumnRebuild).
  • The session reads the table's CREATE, indexes and triggers from sqlite_master, then runs create → copy → drop → rename → recreate in one transaction. Inside a client transaction it uses a savepoint instead.
  • What carries over: data, the inline PRIMARY KEY of a redefined column, constraints, indexes and triggers. Renamed columns are followed in all of them. Type changes re-apply affinity.
  • NOT NULL over existing NULL values fails the statement and leaves the table unchanged.
  • The pure planner is ColumnRebuild::statements in litewire_translate::alter, unit-tested.
• A multi-operation ALTER is split into one statement per operation. Parenthesized ADD (a ..., b ...) and USING BTREE|HASH are handled.

DML

• INSERT IGNORE → INSERT OR IGNORE.
• UPDATE/DELETE ... [ORDER BY] LIMIT n → a rowid IN (subquery) form.
• DELETE t1 FROM t t1 JOIN t t2 ... (the dedup idiom) works.
• UPDATE a JOIN b|(derived) ON ... SET a.x = ... → UPDATE ... FROM.
• UPDATE a, b SET a.x=.., b.y=.. is split into one statement per table. This is only done when each value reads its own table; otherwise it errors.
• || / && are now logical OR / AND. They were string concatenation, so SHOW COLUMNS ... WHERE Field='a' || Field='b' matched nothing. The updater then re-added columns that already existed.

Functions

• New: IF, FROM_UNIXTIME, DATE_SUB/DATE_ADD/d ± INTERVAL n unit, FIND_IN_SET, SUBSTRING_INDEX (counts ±1), and SHOW TABLE STATUS.
• Fix: UNIX_TIMESTAMP(x) ignored its argument and returned text, which sorts after every integer. As a result WHERE t < UNIX_TIMESTAMP() matched every row.

Tests and docs

• Tests: tests/mysql_migration_forms.rs runs on rusqlite and Turso, plus unit tests for each rewrite.
• Docs: docs/sql-translation.md and the CHANGELOG are updated.