Stop repairing project workspace origins

[zccz14]

Summary

• Reject existing project workspaces when their origin differs from the expected resolved project origin.
• Remove automatic git remote set-url origin repair behavior and cover the mismatch path with regression tests.
• Add a changeset noting the safer failure behavior.

Tests

• pnpm exec vitest run --config vitest.workspace.ts --project api modules/api/test/project-workspace.test.ts
• pnpm exec vitest run --config vitest.workspace.ts --project api modules/api/test/project-workspace.test.ts modules/api/test/opencode-session-manager.test.ts
• pnpm --filter @aim-ai/contract run build:dist
• pnpm --filter @aim-ai/api run test:vitest
• pnpm --filter @aim-ai/api run test:lint
• pnpm --filter @aim-ai/api run test:type
• pnpm run test:changeset