MySQL accepts `col INT KEY` as a synonym for `col INT PRIMARY KEY`:
the column gets a real PRIMARY KEY index, NOT NULL is forced on the
column, and a second column carrying bare `KEY` errors at apply
time with `Multiple primary key defined`. Probed:

  CREATE TABLE t (id INT KEY);
  -- SHOW CREATE TABLE t:
  -- CREATE TABLE `t` (
  --   `id` int NOT NULL,
  --   PRIMARY KEY (`id`)
  -- )

myschema's parser previously fell through on `sqlparser.ColKey`
(the vitess enum value for bare KEY), silently dropping the user's
PK declaration: the model had no PRIMARY constraint, no PRIMARY
index, no NOT NULL on the column. The emitted CREATE TABLE
matched the broken model — apply produced a PK-less table, and
the round-trip looked clean because catalog and desired both
agreed on "no PK." The user's intent disappeared without a
single warning.

Fix: add `sqlparser.ColKey` to the `ColKeyPrimary` case in
`applyInlineColumnKey` so both forms share the PK promotion path.
The existing skip-if-PRIMARY-already-set guard handles the
"two columns each with KEY" / "KEY then PRIMARY KEY" precedence
the same way it does for the `ColKeyPrimary × ColKeyPrimary`
case (first column wins; MySQL still rejects at apply time).

Also rewrite the comments on `applyInlineColumnKey` and the
matching call site in `parseCreateTable`. The original comments
claimed `ColKey, ColKeySpatialKey, and ColKeyFulltextKey aren't
valid MySQL column-level attributes`, which was wrong on two
counts:
- `ColKey` is valid (PK synonym, this PR).
- `ColKeySpatialKey` / `ColKeyFulltextKey` are unreachable from
  any valid SQL input — vitess's own grammar rejects the
  column-level shapes (`col GEOMETRY SPATIAL KEY`, `col TEXT
  FULLTEXT KEY`) with a syntax error before
  `applyInlineColumnKey` is reached. The enum values exist as
  defensive carry-over; we leave the arms unhandled rather than
  add errors for an unreachable path (per CLAUDE.md "Don't add
  validation for scenarios that can't happen").

Tests:
- `TestParseInlineColumnBareKeyIsPrimaryKey` (parser): three
  sub-tests pin (a) basic promotion to PRIMARY constraint /
  index / NOT NULL, (b) coexistence with DEFAULT, (c)
  precedence with a later ColKeyPrimary on a different column.
- `testdata/apply/inline_column_bare_key.yml`: end-to-end
  round-trip — desired uses `id INT KEY`, applied DDL emits the
  promoted PRIMARY KEY clause, and `verify_no_drift: true`
  confirms re-plan after apply is empty.

AGENTS.md "In scope (v1)" now spells out that the bare `KEY`
form is honoured as a PRIMARY KEY synonym.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>