Fix primary key migration causing stale schema (#3934)

[clockwork-labs-bot]

Summary

Fixes #3934. Removing or changing a #[primary_key] annotation succeeds on the first re-publish, but the stored schema's table_primary_key field in st_table is never updated. On the next publish, check_compatible fails with:

Primary key mismatch: self.primary_key: Some(ColId(0)), def.primary_key: None

Root Cause

auto_migrate_table handles removing the PK's index and unique constraint, but there was no AutoMigrateStep to update the table_primary_key field in the system table.

Fix

• Add AutoMigrateStep::ChangePrimaryKey variant to the auto-migration planner
• Detect old.primary_key != new.primary_key in auto_migrate_table and emit the step
• Add alter_table_primary_key to the datastore layer (mut_tx, datastore, relational_db) with proper rollback support via PendingSchemaChange::TableAlterPrimaryKey
• Handle the step in auto_migrate_database
• Add migration plan formatter support (termcolor output)

Repro Script

# 1. Publish with primary key
spacetime publish repro --yes  # table has #[primary_key] on name

# 2. Remove primary key — succeeds
spacetime publish repro --yes  # removed #[primary_key]

# 3. Any change — CRASHES
spacetime publish repro --yes  # Primary key mismatch error

Tests

• Unit test in crates/core/src/db/update.rs: Reproduces the exact three-publish sequence from the issue (create table with PK → remove PK → trivial change)
• Smoketest in crates/smoketests/tests/smoketests/auto_migration.rs: Full end-to-end publish flow exercising the same scenario

Files Changed

File	Change
crates/schema/src/auto_migrate.rs	Add ChangePrimaryKey variant + detection
crates/schema/src/auto_migrate/formatter.rs	Format the new step
crates/schema/src/auto_migrate/termcolor_formatter.rs	Colored output
crates/datastore/src/locking_tx_datastore/tx_state.rs	TableAlterPrimaryKey pending change
crates/datastore/src/locking_tx_datastore/mut_tx.rs	alter_table_primary_key
crates/datastore/src/locking_tx_datastore/datastore.rs	Expose through datastore
crates/datastore/src/locking_tx_datastore/committed_state.rs	Rollback support
crates/core/src/db/relational_db.rs	Expose through RelationalDB
crates/core/src/db/update.rs	Handle step + unit test
crates/smoketests/.../auto_migration.rs	Smoketest