fix: harden migration command execution

Two problems in the migration commands: no timeouts, and SQL split on literal
bytes.

`migrations:plan` and `migrations:apply` constructed their connection with
neither a connection deadline nor an operation deadline — a real server reported
`statement_timeout = 0` on the migration connection. Both now default to 10
seconds for the connection deadline, the client query timeout, and PostgreSQL's
own statement_timeout, applied at the one shared construction boundary so a
future call site cannot silently omit them. History reads, advisory-lock
queries, transaction control, migration SQL, and history writes are all covered.
The existing lock-wait deadline, the Pass 2 TLS policy, and Doctor's and the
bootstrap CLI's own timeouts are untouched, and no environment variable or flag
was added.

Explicit client fields do not win under the pinned driver. [email protected].0 builds
parameters as `Object.assign({}, config, parse(config.connectionString))`, so
the URL overrides passed options — verified directly, where an explicit
statement_timeout of 10000 alongside `?statement_timeout=0` produced a
server-reported 0, while a clean URL produced 10s. A DATABASE_URL carrying
connect_timeout, query_timeout, statement_timeout, or an `options` value setting
statement_timeout is therefore refused with the existing fixed configuration
error, before any client is constructed and without echoing the URL, parameter,
or value. Unrelated parameters are left alone.

The runner split each migration on the literal `--> statement-breakpoint` bytes.
Those bytes inside a string literal, a dollar-quoted function body, a quoted
identifier, or a comment tore the migration into fragments that were no longer
valid SQL — each case verified to produce two fragments where one was required.
Each migration's exact SQL is now passed to the client once, with no values and
no prepared-statement name, inside the existing transaction, and its history row
inserted only after that batch succeeds. One transaction still spans all pending
migrations; advisory locking, checksum validation, approval preflight, ordering,
rollback, cleanup, and sanitized error identity are unchanged. The port method
is renamed executeStatement to executeMigrationSql so the contract says what it
receives.

PostgreSQL parses the batch because it owns the only correct parser. A homegrown
splitter would have to track single quotes, dollar quoting with arbitrary tags,
quoted identifiers, line comments, nested block comments, and escape syntax to
answer a question the server already answers, and a parser dependency would add
supply-chain surface for the same reason. Drizzle's marker lines are ordinary
`--` comments when the batch is sent whole. No custom SQL parser exists here.

Co-Authored-By: Claude Opus 5 <[email protected]>

docs/architecture/decisions/README.md

@@ -28,3 +28,4 @@ ADRs capture durable choices that affect more than one package or phase.
 - [0017: Public request perimeter hardening — client address, signup gating, body limits, timeouts](0017-public-request-perimeter-hardening.md) — Accepted
 - [0018: Identity session resolution, canonical public origins, and PostgreSQL transport policy](0018-identity-session-resolution-and-database-transport.md) — Accepted
 - [0019: Durable authorization history and grant management](0019-durable-authorization-history-and-grant-management.md) — Accepted
+- [0020: Module runtime and migration execution hardening](0020-module-runtime-and-migration-execution-hardening.md) — Accepted