fix(Migrator): make HasColumn match the exact column via pragma_table_info

[h2zi]

What this PR does

HasColumn matches the column name as a LIKE substring against the raw table DDL, which reports columns as present when their name merely appears somewhere in the DDL text:

CREATE TABLE plaincols (id integer, first_name text);
-- HasColumn("plaincols", "name") returns true: "first_name text" contains "name "

CREATE TABLE `defv` (`id` integer, `cfg` text DEFAULT 'name value');
-- HasColumn("defv", "name") returns true: the default value contains "name "

When this false positive hits during AutoMigrate, the driver skips AddColumn for a genuinely missing column and later queries fail with no such column.

The fix

Query pragma_table_info instead, which returns the actual columns of the table:

SELECT count(*) FROM pragma_table_info(?) WHERE name = ? COLLATE NOCASE

COLLATE NOCASE keeps the comparison case-insensitive, as the LIKE patterns were. This matches how HasTable and GetIndexes already query metadata instead of searching SQL text.

Tests

TestHasColumnNoFalsePositive covers both false-positive scenarios above plus the positive cases.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes false positives in the SQLite dialector’s Migrator.HasColumn by switching from substring matching against sqlite_master.sql to querying actual table metadata via pragma_table_info, preventing AutoMigrate from incorrectly skipping AddColumn when a column name only appears in DDL text (e.g., as part of another column name or a default string literal).

Changes:

• Replace HasColumn implementation to count exact column-name matches from pragma_table_info(?) using COLLATE NOCASE.
• Add TestHasColumnNoFalsePositive to cover prior false-positive scenarios and confirm true positives.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
migrator.go	Updates HasColumn to check real column metadata via pragma_table_info instead of searching raw DDL text.
migrator_test.go	Adds a regression test ensuring HasColumn does not return true for substring/default-value matches.

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